Which numbers 21 88 126 and 255 are divisible by 7?

To determine which numbers (21, 88, 126, and 255) are divisible by 7, we can use the divisibility rule for 7. According to this rule, a number is divisible by 7 if the difference between twice the last digit and the remaining digits is divisible by 7.

1. 21:

- Twice the last digit (1 * 2) = 2.

- Remaining digits (2)

- Difference = 2 - 2 = 0

- Since 0 is divisible by 7, 21 is not divisible by 7.

2. 88:

- Twice the last digit (8 * 2) = 16.

- Remaining digits (8)

- Difference = 16 - 8 = 8

- Since 8 is not divisible by 7, 88 is not divisible by 7.

3. 126:

- Twice the last digit (6 * 2) = 12.

- Remaining digits (12)

- Difference = 12 - 12 = 0

- Since 0 is divisible by 7, 126 is divisible by 7.

4. 255:

- Twice the last digit (5 * 2) = 10.

- Remaining digits (25)

- Difference = 10 - 25 = -15

- Since -15 is not divisible by 7, 255 is not divisible by 7.

Therefore, the only number that is divisible by 7 in the given set is 126.