21.If the mean of A, B, C, D and E is 50 and mean of B, C, D and E is 60, then the value of A is

The mean of B, C, D and E is 60. This means that the sum of B, C, D and E is 60 * 4 = 240.

We know that A is not included in the sum of B, C, D and E, so the value of A must be 250 – 240 = 10.

Option (b) is incorrect because 15 is not a multiple of 5.

Option (c) is incorrect because 20 is not a multiple of 5.

Option (d) is incorrect because 25 is not a multiple of 5.