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The no.s (a,b,c) are selected by throwing a dice thrice.then the probability that (a,b,c) are in A.P. is? i am geting the ans to be 18/216 but the ans is 21/216

The no.s (a,b,c) are selected by throwing a dice thrice.then the probability that (a,b,c) are in A.P. is?


i am geting the ans to be 18/216 but the ans is 21/216

Grade:11

3 Answers

Ashwin Muralidharan IIT Madras
290 Points
10 years ago

Hi Debadutta,

 

(a,b,c) can be

(1,2,3) -------- 2 possibilities (3,2,1) is the other order

(2,3,4) -------- 2 possibilities

.....     --------- -do-

.....

(4,5,6) -------- -do-

 

it could be

(1,3,5) -------- 2 possibilities

(2,4,6) -------- 2 possibilities

 

or it could be

(1,1,1)

(2,2,2)

....

....

(6,6,6).

 

So total number of ways = 2*6 + 6 = 18.

 

Your answer is very fine.

Have confidence in your working. It helps for competitive exam prearation.

21/216 is not the right answer.

 

Regards,

Ashwin (IIT Madras).

Sathya
35 Points
10 years ago

How can This be an A.P.Minimum C.D for an AP is 1.

(1,1,1) (2,2,2)........(6,6,6).

SIBASHIS MAHAPATRA
14 Points
10 years ago

the answar is  18/216, there cant be more than 18 combos of AP for 3 die

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