gmatmember85 wrote:

If a fair coin marked 1 and 2, and a fair die are rolled together, what is a probability to have the sum even?

a) 1/8 b) 1/4 c) 1/2 d) 3/4 e) 7/8

Ans: C..

I've a question here. So I understand the total outcomes is 2*6 = 12

When the sum is even, we have 1+1, 1+3, 1+5, 2+2, 2+4, 2+6 = 6

so we say probability is 6/12=1/2 .. however, I'm unable to make a difference of when to use the favorable events like 1+1, 1+3, 1+5, 2+2, 2+4, 2+6, 1+1, 3+1, 5+1, 2+2, 4+2. 6+2 .. Since both are rolled together, why don't we consider the other possibilities??

Could someone please explain?

the total number of combinations is 12 ( 2 from coin and 6 from dice)

the favourable combinations are

for 1 in coin, 1,3 & 5 should be in dice - so 3 combinations

for 2 in coin, 2,4 & 6 should be in dice - so 3 combinations....together 6 combinations are favourable...

so favorable/total -> 6\12 -> 1\2 -> C is the answer

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Regards,

Harsha

Note: Give me kudos if my approach is right , else help me understand where i am missing.. I want to bell the GMAT Cat

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