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[GHong14]

If a and b are both single-digit positive integers, is a + b a multiple of 3?

(1) The two-digit number "ab" (where a is in the tens place and b is in the ones place) is a multiple of 3.

(2) a - 2b is a multiple of 3.

D

[DeepthiRajan]

Hi

Its easy to solve by plugging in numbers:

1. ab is a multiple of 3. You can take any two digit multiple of 3 starting from 12 onwards and you will see that in all the cases
a+b is also divisible by 3. SUFF

2. a-2b=divisible by 3;again you can plug in numbers such as

7-2(2)=3; a=7 b=2 and 7+2=9 ----->multiple of 3
5-2(1)=3; a=5 b=1 and 5+1=6 ----->multiple of 3
SUFF

Hence D. HTH

[Rahul@gurome]

If a and b are both single-digit positive integers, is a + b a multiple of 3?

(1) The two-digit number "ab" (where a is in the tens place and b is in the ones place) is a multiple of 3.
(2) a - 2b is a multiple of 3.

Statement 1: From the rule of divisibility by 3, we can easily conclude that if the two-digit number "ab" (where a is in the tens place and b is in the ones place) is a multiple of 3, then (a + b) is also a multiple of 3.

Sufficient

Statement 2: a - 2b is a multiple of 3
Now we can write (a - 2b) as (a + b - 3b).
Thus (a + b - 3b) is a multiple of 3, which is obtained by subtracting 3b (which is also multiple of 3) from (a + b).
Hence, (a + b) is also a multiple of 3.

Sufficient

The correct answer is D.