Bunuel
If a and b are integers, is 3a + 5b divisible by 26?
(1) a is divisible by 13
(2) 13 is a factor of b
Solution:
• Given, a and b are integers.
We need to find whether 3a + 5b is divisible by 26.
Statement 1: a is divisible by 13
• Then, 3a is divisible by 13 but we do not have any information about b.
Hence, statement 1 is not sufficient and we can eliminate the answer options A and D.
Statement 2: 13 is a factor of b
• This means that b is divisible by 13. Thus, 5b is divisible by 13 but we do not have any information about a.
Hence, statement 2 is not sufficient and we can eliminate the answer option B.
Combining Statement 1 and Statement 2:
From Statement 1: 3a is divisible by 13
From Statement 2: 5b is divisible by 13
This implies, 3a + 5b is divisible by 13.
Let us consider few cases as follows:
• If 3a + 5b = 13, then 3a + 5b is not divisible by 26.
• If 3a + 5b = 26, then 3a + 5b is divisible by 26.
Thus, on combining both the statements, we get two contradictory results. Hence, the correct answer is
Option E.