A sprox?

Probability Level 3

Mr Meaner met Miss Demeanor and together they committed a crime...

Mr M stole socks, Ms D stole a sprox, and now they're serving time.

The sprox and the socks were put in a box and three were pulled out at random.

If the probability of picking three socks, is the same as the sprox and two socks,

Then how many socks were stuck in the box with the sprox?

4 It's impossible 2 6 5 7 1 3

Geoff Pilling by Geoff Pilling , 53, USA

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1 solution

Geoff Pilling
Apr 12, 2019

Essentially the problem boils down to how many items need to be in the box so that the probability that the sprox is one of the three items is 50/50. Clearly this means there must be six items. Since one is the sprox, 5 must have been socks.

1 Helpful 1 Interesting 2 Brilliant 0 Confused

nC3 = (1C1) × nC2
nC3 = 1 × nC2 = nC2
n = 3 + 2 = 5

Saya Suka - 2 months, 1 week ago

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