Rank four businesses from best to worst investment in one hour with quick maths: Palvin Pipes (ROIC 15%, growth 10%, P/E 18), Serik Software (ROIC 40%, growth 20%, P/E 45), Morvanti Hotels (ROIC 7%, growth 8%, P/E 30), Juvara Dairy (ROIC 18%, growth 6%, P/E 14). Use earnings yield plus growth adjusted for reinvestment.

Ranked by implied owner's return: Serik about 21%, Palvin 11.9%, Juvara 10.8%, Morvanti 7.5%. Growth costs reinvestment equal to growth divided by ROIC, so high-return businesses keep more of their earnings yield. That turns the P/E ranking upside down for Serik. Its lead depends on its 45x multiple holding: if the multiple falls to 25x over five years, its return drops to about 8%. Morvanti must raise money to grow at a 7% return, which destroys value.

A farmer who wants a bigger harvest next year keeps back more seed this year; how much he must keep back depends on how many grains each seed yields. To grow earnings by g, a business must reinvest the share g / ROIC of its earnings, so a high return on capital makes growth cheap and a low one makes it expensive. Serik grows 20% by reinvesting 20 / 40, half its earnings. Palvin reinvests 10 / 15, two thirds. Juvara reinvests 6 / 18, a third. Morvanti would need 8 / 7, 114% of its earnings, more than it makes, so it must raise outside money to grow.

By P/E alone the order is Juvara, Palvin, Morvanti, Serik: cheapest first. A P/E prices one year of earnings but not what it costs to grow them, so it flatters businesses whose growth is expensive and punishes those whose growth is cheap. Juvara's 7.1% earnings yield looks best, but it grows only 6%. Palvin's 10% growth absorbs two thirds of its 5.6% yield. Morvanti looks like a growth stock at 30x, but at a 7% return on capital, likely below its cost of capitalThe return investors require for the risk of a business. Growth earning less than it destroys value., say 11%, every rupee it reinvests is worth less than a rupee, so its growth destroys value rather than creating it.

The formula assumes each P/E stays where it is and each growth rate lasts. That is most doubtful for Serik. If Serik's growth slows and its P/E falls from 45x to 25x over five years, the lower multiple costs about 11% a year, and its return drops to about 8%, below Palvin and Juvara. So the honest ranking says Serik first, if its high returns on capital and growth last long enough to justify 45x, and names that as the question to answer next. Palvin and Juvara are close enough that the ranking between them could flip on a small change in growth, which is worth saying rather than hiding.

In the room, present it in this order: the ranking, the one formula, the insight that growth is cheap only when returns on capital are high, and the risk to the top pick. With one hour and one line per company, the interviewer is scoring whether you choose a sensible framework quickly and know where it breaks, not whether you reach a precise number.