Probability-Ice cream

[sulabh]

There are only three varities of ice creams in Jokaland priced at Rs 5,Rs 10 and Rs 15.If, Arun buys 4 ice creams for Rs 45 from Jokaland, then what is the probability that any two of them together will cost exactly Rs 20 ?

A.1/2
B.1/4
C.3/4
D.3/8
E.5/12

Answer and my explanation after discussion.

[TrizMA]

is answer E: 5/12?

Only two comibination of 4 ice cream for Rs.45 are possible

i) 5,10,15,15
ii) 10,10,10,15


i)5,10,15,15
total 6 combination possible. two combinations give 20

ii) 10,10,10,15
total 6 combination possible. three combinations give 20


Total desired combinations=5
Total combinations=12

prob=5/12

pls tell if it's correct

[sulabh]

Yup thats right.

[TrizMA]

sulabh, u wrote:

i)5,10,15,15
total 6 combination possible. 3 combinations give 20

pls show three combinations which give 20.

i can only count 2 combinations. 1)5,15 2)5,15.

what's the third combination which gives 20?

If OA 1/2, then there must be some other approach to this. What's the OA?

[TrizMA]

sorry sulabh, my bad. a blopper

[beeparoo]

There are only three varities of ice creams in Jokaland priced at Rs 5,Rs 10 and Rs 15.If, Arun buys 4 ice creams for Rs 45 from Jokaland, then what is the probability that any two of them together will cost exactly Rs 20 ?

A.1/2
B.1/4
C.3/4
D.3/8
E.5/12

Answer and my explanation after discussion.

Did you make up this question, sulabh? If so, I have some questions for you.