how do you calculate log base 1.1 (1000) = ? on the calculator. the answer is 72.5, but I dont know how to get this answer.

Enter  log(1000,1.1)

i.e. enter log(number, base)

.

Thanks Alan,

Or if you are using a different calculator you can use the change of base rule

$$log_{1.1} (1000) =\frac{log1000}{log1.1}$$

you can use any base you like :)

$${\frac{{log}_{10}\left({\mathtt{1\,000}}\right)}{{log}_{10}\left({\mathtt{1.1}}\right)}} = {\mathtt{72.476\: \!573\: \!784\: \!290\: \!347\: \!8}}$$