Question

A handbag contains seven coins and three

keys. Two items are taken out of the handbag
one after the other and not replaced. Find
the expected number of keys taken out of the
handbag

Answer 1

0.59998

Explanation:

Number of keys = 3

Number of coins = 7

Total = 10

Number of items taken out = 2

Expected number of keys taken out:

Let x = Number of keys taken out

X = 0

1st pick = 7/10

2nd pick = 6/9

7/10 * 6/9 = 0.46666

X = 1

(7/10 * 3/9) + (3/10 * 7/9) = 0.46666

X = 2

(3/10 * 2/9) = 0.066666

X : ____ 0 ______ 1 _______ 2

P(X): _0.46666__0.46666 _0.06666

Expected value :

(0*0.46666) + (1*0.46666) + (2*0.06666)

= 0.59998