I Would Guess...?

A weekly estimation challenge for Delhi University students. Three questions, three difficulties, no calculators required - just a working and a willingness to be roughly right.

What's a guesstimate? · Jump to this week's set

What's a guesstimate?

A guesstimate is an estimate you build from scratch, out loud, using only what you already know. Nobody expects you to know how many chai stalls there are near North Campus - but you can reason your way to a number that's in the right neighbourhood, and show exactly how you got there.

It's the core skill tested in consulting and finance case interviews, and it's a useful habit well beyond that: breaking an unfamiliar, unmeasurable question into small pieces you can actually reason about.

Break it down - split the big unknown into smaller, guessable pieces.
Estimate each piece - use whatever you genuinely know: population, rough averages, your own experience.
Put it back together - multiply the pieces back into one number.
Sanity-check the size - does it feel like the right order of magnitude, or off by a factor of ten?

Worked example - how many piano tuners are there in Delhi?
Start from Delhi's population (~3 crore), guess how many households own a piano (maybe 1 in 2,000), and how often each gets tuned (once a year). That's roughly 15,000 tunings a year. If one tuner can do about 500 tunings a year, that's around 30 piano tuners in the city. The exact number matters less than the fact that every step is defensible.

Toolkit

Bottom-up decomposition - build the number from small units up: people, then households, then a city.
Top-down anchoring - start from a number you're confident about and adjust from there.
Round aggressively - 10, 100, 1,000. Precision isn't the point; the chain of logic is.
Say your assumptions out loud - a guesstimate is a chain of assumptions, not a lucky number.

Want more reps before this week's set? Try these on your own:

How many textbooks change hands in Kamla Nagar market every semester?
How many cups of tea does a DU college canteen pour in one academic year?
How many hours does the average DU student spend on the metro per week?

This week's set

Solve Easy first - it unlocks Medium, and Medium unlocks Hard. Each question is broken into pieces already - fill in a number for each piece and a one-line reason it's about right, and we'll multiply them together for you. Lock it in, add your name and email once, and it carries over to the rest of the set.