Cianplan

Level 1: Foundations · L1.4 Back-of-the-envelope estimation & numbers to know

Estimation drills (mixed practice)

Solve 4 timed estimates and use the result to make a design decision.

15 min · Free

What you take away

  • An estimate exists to rule options out, so it is not finished until you say what it rules out.
  • State your assumptions before the arithmetic — they are what an interviewer can agree with or correct.
  • One significant figure, aggressive rounding, and the units written down at every step.
  • If the answer sits within 10× of a rung boundary, tighten one assumption rather than the arithmetic.

How the class is laid out

  1. The point of estimating
  2. The method, in four moves
  3. Anchors
  4. Time
  5. QPS chain
  6. Storage and bandwidth
  7. The habit
  8. The drills
  9. After a drill