Find number of digits in `18^20`

If log2=0.30103, then the number of digit in 5^(20) is a.14 b.16 c.18 d.25

If log2=0.30103, the number of digit is 2^(64) is a.18b.19c.20d.21

Find the sum of digits of range of data : 13, 18, 20, 15, 12, 17, 9, 14, 11 and 16

If the number obtained on the interchanging the digits of two-digit number is 18 more than the original number and the sum of the digits is 8, then what is the Reversed number?

If the number obtained by interchanging the digits of a two digit number is 18 more than the original number and the sum of the digits is 8 then what is the original number?