GWD20-14

meckychen

Q14:

Six cards numbered from 1 to 6 are placed in an empty bowl.  First one card is drawn and then put back into the bowl; then a second card is drawn.  If the cards are drawn at random and if the sum of the numbers on the cards is 8, what is the probability that one of the two cards drawn is numbered 5 ?

A1/6  B1/5 C1/3 D2/5 E2/3

Answer is D,

How to calculate?

Thank you.





Answer:

gyhehe

This is what i thought.
The easiest way to do it is to find its sample space, which is  {(2,6),(3,5),(4,4),(5,3),(6,2)}.  FIVE appears twice, thus we can obtain the final answer -- 2/5.
Hope it helps~

meckychen

yes, thank you.