Which of the following numbers is divisible by 6?
- (a)62233
- (b)438750
- (c)12581
- (d)128530
Answer
Why
Correct — B. Divisible by 6 means divisible by 2 and by 3 — both tests, every time.
Test for 2: 438750 ends in 0, so it is even.
Test for 3: its digit sum is 4+3+8+7+5+0 = 27, a multiple of 3.
Both pass, so 438750 clears 6 → option (b). Direct check: 438750 ÷ 6 = 73125.
Why the others are wrong
- (a)62233 — 62233 ends in 3. An odd number fails the test for 2 straight away, and no odd number is divisible by 6 however its digits add up.
- (c)12581 — 12581 ends in 1, odd again, so it fails the same test for 2. Its digit sum, 17, is not a multiple of 3 either.
- (d)128530 — 128530 is even, which is what makes it tempting, but its digit sum is 1+2+8+5+3+0 = 19, not a multiple of 3. It is divisible by 2 and by 5, not by 6.
Concept
A number is divisible by 6 exactly when it is divisible by 2 and by 3 at the same time, because 2 and 3 are coprime and their product is 6.
The two tests are independent and both are cheap: read the last digit for 2, add all the digits for 3.
That cheapness is the trap. An even number is only half-qualified, and running one test instead of two is how a ten-second mark is lost.
The same two tests, set the harder way round, ask you to supply a missing digit rather than pick a whole number — 217924k at 09 Sep 2024, 09:00, Quant Q.11 and 249k876 at 17 Sep 2024, 09:00, Quant Q.20.
Key facts
- Divisibility by 6 needs both tests to pass: the last digit even, and the digit sum a multiple of 3.
- 438750 has digit sum 27 and 438750 ÷ 6 = 73125.
- 128530 is divisible by 2 and by 5 but not by 3, so it is not divisible by 6.
- Failing either test is enough to rule a number out for 6.
Study next
Common traps
- Stopping at even — 128530 is even and still not divisible by 6.
- Misadding a six-digit digit sum. Recount 4+3+8+7+5+0 = 27.
- Assuming a number ending in 0 must clear 6 because it clears 10.
SSC sets this both ways: pick the divisible number from four, as here, or supply the missing digit. The missing-digit form is asked at 09 Sep 2024, 09:00, Quant Q.11 (217924k) and 17 Sep 2024, 09:00, Quant Q.20 (249k876), and both still come down to the 2-test and the 3-test run together.
Related PYQs
No directly related past PYQ was found.