How many digits does the product of 4^15 and 5^29 contain?
A. 12
B. 13
C. 23
D. 30
E. 35
So our aim is to find how many digits will the product of the above numbers have ie ,
4^15 X 5^29
= (2^2)^15 X 5^29
= 2^30 X 5^29
= 2X 2^29 X 5^29
= 2 X (2 X 5)^29
= 2 X 10^29
so the answer is 30 digit number