If a and b are prime numbers, what is the value of a*b?

Question

(1) a - b = 1
(2) a = 3

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zhanbo · Answer

(1) Only
a=3 & b =2
(If b is not 2, it has to be an odd number. a is also an odd number. So a-b can never be 1.)
Sufficient

(2) Only
No info on b
Not sufficient.

The answer is thus  (A) .

8.toastcrunch · Answer

statement 1 :   a - b = 1, we know that 2 and 3 are only consecutive prime numbers , so a =3 and b = 2 
 Sufficient

statement 2 :  a = 3 , we do not know the value of b ,it can 3 ,5,7.......
 Insufficient

A is the answer.

hinasingh · Answer

If a and b are prime numbers, what is the value of a*b?
(1) a - b = 1
As we know, 2 and 3 are the only consecutive prime numbers, so a*b = 6 and it does not matter whether a = 2 or 3, as we need to find the product a*b. 
Sufficient
(2) a = 3
No information on b. Hence, not sufficient

answer A

walterwhite756 · Answer

Pre-requisite : For solving this question, you only need to keep in mind that  only two consecutive prime numbers are 2 and 3 .

Stmt A: If  a-b = 1 , means they are consecutive and hence 2 & 3, therefore  a*b = 6 , hence  sufficient .
Stmt B: If  a = 3 , value of b can not be ascertained since b can be any prime number and hence  a*b  can not be ascertained. Hence  insufficient .

Therefore   Option A is the answer  .

rxb266 · Answer

If a and b are prime numbers, what is the value of a*b?

(1) a - b = 1
the only set of 2 prime numbers with a difference of 1 is (2,3). Hence a x b = 6. SUFFICIENT

(2) a = 3

here b can be any prime number. NOT SUFFICIENT

Ans: Option A

If a and b are prime numbers, what is the value of a*b?

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GMAT Data Sufficiency (DS) Questions

If a and b are prime numbers, what is the value of a*b?

Prep Toolkit

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