Wednesday, 19 October 2011

P & C - 2 (SNAP-2008)

A number lock consists of 3 rings each marked with 10 different numbers. In how many cases the lock can not be opened
(A)  310        (B)  103        (C) 30        (D) 999   (E) none

Solution follows here:

To open the lock, we need to fix one number in each of the three rings. Given that each ring has 10 different numbers.
All possibilities for the first ring = 10
All possibilities for the second ring = 10
All possibilities for the third ring = 10
These three are independent activities.
From fundamental principle, all possibilities = 10 * 10 * 10 = 1000
But out of all these, only one possibility can open the lock and rest 999 possibilities can not open the lock.
Answer (D)

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