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Interview Question

Interview Mountain View, CA

How many ping pong balls fit in a school bus?


Interview Answer

2 Answers


There's a few things I would clarify with the interviewer before starting but I'll spare you for now. Let's start with the size of the balls, that we assume will have a radius of 2cm. To account for the gap between balls when filling a space, we will also assume that the balls take up the space of a 4cm x 4cm cube (16cm3). At the end we will also add an extra ball for every 4 balls to account for the gap neglected in assuming a cube. To keep things simple, we assume we have nothing inside (no seats, etc). In guesstimating the dimensions of the bus we'll say each seat would be 3.5ft long while the center aisle is 1.5ft for a total width of 8.5ft. We'll also guess that a bus is about 40ft long and 8ft tall. This brings our net volume to: 2,720ft3. 1ft ~ 30.5cm 2,720ft3 ~ 77,021,823cm3 77,021,823cm3 / 16cm3 ~ 4,813,864 balls Accounting for gap: 4,813,864 / 4 ~ 1,203,466 balls Net total: 4,813,864 + 1,203,466 = 6,017,330 balls

Luca on Jul 31, 2013

Another ridiculously detailed answer can be found at > http://www.nab.bz/bus-explanation.pdf This is not my work, just found it while preparing.

Luca on Jul 31, 2013

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