A number, divided by 987, gives a remainder 59. When the same number is divided by 21, what is the remainder?

When number N is divided by 987, remainder is 59. This means N = 987k + 59 for some integer k. To find remainder when N is divided by 21, we need (987k + 59) mod 21. Since 987 = 21 × 47 (987 is divisible by 21), 987k mod 21 = 0. So N mod 21 = 59 mod 21. Dividing 59 by 21: 21 × 2 = 42, remainder = 59 - 42 = 17. The remainder is 17. Option A (21) is impossible since remainder must be less than divisor.