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Google Associate Product Manager Interview Question

I interviewed in Mountain View, CA and was asked:
"How many ping pong balls fit in a school bus?"
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Part of a Associate Product Manager Interview Review - one of 3,037 Google Interview Reviews

Answers & Comments

0
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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
1
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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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