@Arjun Sir,Wouldn't the powers of 2 be 2^{0},2^{1},2^{2},2^{3} instead of 2^{4}. Similarly for 5 d powers be 5^{0},5^{1},5^{2},5^{3} instead of 5^{4 }.Tat is how 4 options for 2 and 5 respectively. So for Numerator part 4X4 respectively. Similarly for 2^{99 }and 5^{99}. The denominator wud give 100 X 100. Hence 16/10000=1/625