What is ##log 100 + log 10##?

##3##

As we know

##log A+log B = log(A * B)##

This means that you can write

##log(100) + log(10) = log(100 * 10)##

##=log(1000)##

##=log(10^3)##

Since

##log(x^n) = n* log(x)##

you can say that

##log(10^3) = 3 * log(10) = 3 * 1 = 3##