Every case has a moment when the numbers stop and the interviewer asks something open: what could be driving this, how else could the client grow, what are the risks, what would you want to know. Candidates who have drilled the maths often go quiet here, or list ten things in no order and lose the points anyway. This deck is about those questions. It covers how they are scored, the habit of naming buckets before ideas, four spines you can hang a brainstorm on, the so what rule, prioritising with a two-by-two, writing a hypothesis that could actually be wrong, and recovering when the interviewer says what else. It ends with one full brainstorm run end to end. Case Structuring covers the opening structure; this deck covers what happens after it.
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Card 1 of 16
Halfway through a case the interviewer leans back and asks, “what could be driving the decline?” There is nothing on the table to analyse. What kind of question is this, and how is it actually being marked?
A brainstorming question is scored on breadth in organised buckets first, then depth on one or two ideas.
A brainstorming question is an open prompt with no data behind it: what could cause this, how else could the client grow, what are the risks, what would you want to know. The interviewer is not counting ideas. They are scoring two things, in order. First, breadth: did you cover the whole space by grouping ideas into a few named categories, called buckets, rather than firing off whatever came to mind. Second, depth: when asked to pick one, could you explain why it matters and roughly how big it is. A candidate with three buckets and six ideas beats one with twelve unsorted ideas, every time.
Card 2 of 16
A gym owner asks how she could raise revenue. Show me the “buckets first, then ideas” technique on that question, out loud, the way you would in the room.
Name the buckets before any idea, then give two ideas per bucket so every idea has an address.
Start by saying the categories, not the ideas: revenue can come from existing members, from new members, or from things that are not a membership at all. Only then fill each one. Existing members: raise the monthly price on the top tier, and sell add-ons like personal training. New members: a referral reward for bringing a friend, and an off-peak daytime plan for people who work from home. Non-membership revenue: rent the studio to yoga instructors in quiet hours, and open the café to the public. Six ideas, but the interviewer hears a map, and can see at a glance that nothing obvious has been missed.
Card 3 of 16
Ferrow Retail’s like-for-like sales have slipped for three quarters and the interviewer asks what could be behind it. What is the simplest first split you can reach for, and why does it work?
Internal is what the client controls, external is the market around it, and together they cover everything.
Internal versus external is the most reusable pair of buckets in a case. Internal causes are things inside Ferrow’s own walls: pricing decisions, range changes, store staffing, a website relaunch that went badly, a closed distribution centre. External causes are things happening to every retailer at once or arriving from outside: a new competitor opening nearby, a shift in what shoppers want, weaker household budgets, new regulation. The split works because the two halves genuinely do not overlap, and because they point to different fixes. An internal cause the client can reverse; an external one it has to respond to.
Card 4 of 16
Overton Digital sells accounting software on a monthly subscription and wants more revenue. You have offered the usual buckets. What is the customer journey, and how does it surface ideas you would otherwise miss?
Walk the customer from awareness to purchase to use to renewal, and ask what could improve at each step.
The customer journey is the sequence of steps a customer goes through with a business, and it makes a spine for brainstorming: you hang ideas on each step in order. For Overton, awareness: partner with accountants who recommend software to small firms. Purchase: a free trial that converts to paid without a sales call. Use: prompts inside the product that steer new users to the features that make them stay. Renewal: an annual plan at a discount, so the cancel decision comes once a year rather than twelve times. Because the spine has an order, the interviewer can follow it, and you cannot skip a step without noticing.
Card 5 of 16
Talbrook Industries makes industrial pumps and its margins are being squeezed. The interviewer asks where cost could be taken out. Walk me through the value chain as a way to organise your answer.
The value chain lists the steps that turn inputs into a sold product, and each step is a place cost can hide.
The value chain is the chain of activities a business performs to make and sell what it sells: buying inputs, making the product, moving it, selling it, and supporting customers afterwards. Used as a spine, it forces a cost brainstorm to cover every stage. Inbound: fewer suppliers with volume discounts, and less steel scrap. Operations: scheduling to cut changeover downtime, and energy contracts. Outbound: fuller lorries and fewer depots. Sales: move small accounts to online ordering. After-sales: remote diagnostics before sending an engineer. Not every idea will be right; the point is that the interviewer sees you have walked the whole path from the factory gate to the customer’s door.
Card 6 of 16
Halstead Foods sold 8% fewer cases of its frozen range last year and the interviewer asks why that might be. Why is supply versus demand a better spine here than internal versus external?
Fewer people wanted it, or the client could not get it to them, and those are two different problems.
A volume fall has two possible shapes. On the demand side, customers wanted less: a price rise pushed them to a rival, a trend away from frozen food, a supermarket delisting the range, a competitor launching first. On the supply side, customers wanted it but could not get it: a factory line down, a packaging shortage, a haulier contract that failed, stock sitting in the wrong depot. Internal versus external would scatter these across both halves. Supply versus demand keeps each cause next to its fix, and the first data request follows straight from it: were the shelves empty, or were the products on the shelf and not moving.
Card 7 of 16
Marlstone Capital, a private equity fund, is about to buy Kestrel Components, and the partner asks you for the risks of the deal. How do you use stakeholders to make sure the list is complete?
Ask who touches the business, customers, rivals, regulators, suppliers, staff, and what each could do to it.
A stakeholder is anyone with a stake in what the business does, and each group is a source of risk you can name in turn. Customers: Kestrel’s top three accounts might use the change of owner to renegotiate or leave. Competitors: a rival could poach those accounts while management is distracted. Regulators: the competition authority could delay clearance, or a safety standard could change. Suppliers: a sole-source supplier could raise prices once it knows a fund is paying. Employees: the founder’s engineers might walk if their share options are cashed out. Five groups, five distinct risks, and nothing depends on remembering a clever idea under pressure.
Card 8 of 16
You have just given the interviewer ten ideas for growing Calder Foods and she says nothing, waiting. What is missing from your answer, and what is the “so what” rule?
Every idea earns one extra line saying why it matters and roughly how big it could be, or it is only a word.
An idea with no so what is a noun. ‘Enter food service’ tells the interviewer nothing about whether it is worth doing. The so what rule adds one sentence per idea covering two things: why it matters for this client, and a rough size. ‘Enter food service: restaurants buy in bulk with lower marketing cost, and if we won 5% of a £2bn channel that is £100m, a fifth of today’s £500m revenue.’ The size can be a guess, and you should say so, but naming a number turns a list into a judgement. It also shows the interviewer which ideas you would pursue before she asks.
Card 9 of 16
Back to the gym. You have six revenue ideas on the table and the interviewer says, “we have ten minutes, which two should we work on?” How do you choose without it sounding like a coin toss?
Score each idea on impact and ease, pursue the high-impact easy ones, and say why the others wait.
Draw a two-by-two in your head: one axis for impact, how much revenue the idea could add, the other for ease, how quickly and cheaply it could be done. Add-on personal training is high impact and easy, the trainers are already there, so it goes first. Studio hire is easy but small, a quick win to mention and move on. A top-tier price rise is high impact but risks losing members, so it needs a test. The public café is low impact and needs planning permission, so it waits. Pick two from the top-left and say the rule out loud, so the interviewer sees the choice was made, not felt.
Card 10 of 16
Northbay Logistics’ profits have fallen and the interviewer asks for your hypothesis. You say “I think costs have gone up.” Why is that a weak hypothesis, and what does a strong one look like?
A hypothesis is a testable sentence: profits fell because X, which we would see as Y in the data.
A hypothesis is a guess you commit to so it can be tested. ‘Costs have gone up’ cannot fail, because something always has, and it points to no data. A testable version has the shape ‘profits fell because X, which we would see as Y in the data.’ For Northbay: ‘profits fell because diesel and driver pay rose faster than the prices it charges, which we would see as cost per delivery rising while revenue per delivery stayed flat.’ Now it can be wrong: if revenue per delivery fell too, it is a pricing story. Falsifiable means a specific number could disprove it, and that is what makes it useful.
Card 11 of 16
Your hypothesis is that Northbay’s cost per delivery has risen. The interviewer says, “fine, what do you want from me?” What do you ask for, and how do you phrase it so it sounds like a consultant rather than a shopping list?
Ask for the smallest cut of data that could prove the hypothesis wrong, and say what you expect to see in it.
Work backwards from the sentence. If cost per delivery rose, the data that shows it is total cost divided by deliveries, this year against last, split into the lines you suspect: fuel, driver pay, vehicles. So the ask is ‘cost per delivery for the last two years, split by fuel, labour and fleet, and I expect fuel and labour to explain most of the rise.’ Saying what you expect lets the interviewer hand you an exhibit that confirms or kills the idea in one look. Asking for ‘all the financials’ shows you have not decided what you are testing, and it is the commonest way a good hypothesis gets wasted.
Card 12 of 16
You have given four solid ideas for lifting Windmere Foods’ margins and the interviewer says “what else?” Your mind is blank. What are the three recovery moves, in the order you would try them?
When you run dry: change lens, go up a level, or move to another stakeholder, and name the move out loud.
Silence is not the problem, scrambling is. Three moves reopen a list. First, change lens: if you were on cost ideas, switch to revenue, or from price to volume, and say so, ‘so far I have been on costs, let me look at the revenue side.’ Second, go up a level: instead of ideas for this product, ask what the company could do with the factory, the brand or the customer list. Third, move to a different stakeholder: what would suppliers, retailers or the regulator let Windmere do differently. Naming the move buys five seconds and shows the interviewer the blank was momentary, not the bottom of the well.
Card 13 of 16
Corrigan Foods wants to launch a premium ready-meal range through supermarkets. The interviewer asks for the risks. Why should every risk arrive with a mitigation attached, and what does that sound like?
Say each risk and its mitigation in one breath, so the list reads as a plan rather than a list of worries.
A risk on its own is a reason not to act. A risk paired with a mitigation, the action that reduces its chance or its cost, is a decision the client can make. For Corrigan: the new range cannibalises its existing meals, mitigated by pricing it clearly above and keeping the old range on shelf. Supermarkets refuse to list it, mitigated by piloting with two chains before committing the plant. The single packaging supplier cannot scale, mitigated by qualifying a second supplier before launch. Three pairs, each with a rough size in mind, and the interviewer hears someone who would still be useful the week after a launch went wrong.
Card 14 of 16
A partner tells you the candidates she remembers are the ones who offered one idea nobody else did. What is the “unusual idea”, when do you offer it, and how do you stop it sounding like a gimmick?
Offer one unexpected, commercially grounded idea after the obvious ones, and size it like any other.
The unusual idea comes from thinking about the client’s actual position rather than the framework: a gym selling its class-demand data to equipment makers, Halstead Foods renting spare freezer capacity to a rival, Northbay letting customers book an empty return leg at a discount. It goes last, after the expected buckets are covered, never first, because offered early it looks like you skipped the basics. It has to pass the so what test like anything else: who pays, roughly how much, what it would need. One is plenty. Two starts to sound like someone who cannot tell a business from a brainstorm.
Card 15 of 16
You have brainstormed for four minutes on Bramwell & Co.’s growth options and the interviewer says, “so, where does that leave us?” What does a good closing synthesis of a brainstorm contain, and how long is it?
Close in three lines: the buckets covered, the two ideas you would pursue, and the first thing you would do.
A brainstorm without a close is a pile. The synthesis takes thirty seconds and has three parts. The buckets, named again so the interviewer hears the coverage: ‘growth could come from existing clients, new clients or new services.’ The two ideas you would pursue, with the so what attached: ‘I would start with cross-selling the advisory service to existing clients, worth perhaps £3m, and a referral partnership with regional accountants.’ The first step: ‘the first thing I would do is pull revenue per client for the top fifty to see how many already buy more than one service.’ Coverage, choice, action, and then stop talking.
Card 16 of 16
NorthPeak Airlines, a regional carrier, wants to lift revenue per passenger from its current £90 average. Run the whole brainstorm for me, end to end: buckets, ideas, sizes, the two you would pursue, a hypothesis and a first step.
Three buckets, six sized ideas, two chosen on impact and ease, one testable hypothesis and one first step.
Buckets: the fare itself, extras around the flight, and revenue beyond the ticket. Fare: peak-day pricing, a flexible tier. Extras: paid seat selection, a second bag tier. Beyond the ticket: hotel commissions, a co-branded card. Sizing against £90: a 10% rise on the busiest 30% of flights adds about £3, £6 seat selection taken by one in three adds £2, hotel commission perhaps £1, about £6 in all, near 7%. I would pursue seat selection and peak pricing: biggest, and quickest to switch on. Hypothesis: business-route passengers will pay for seats, seen as take-up above 30% in a two-route pilot. First step: route load factors, then the pilot.
Reading is not the same as remembering. Study this deck with scheduled review so the cards come back before you forget them.