Question

Which expression is equivalent to 5^-2 x 5^-1

Answer 1

When you multiply powers with the same base, you sum the exponents:

$a^b\times a^c=a^{b+c}$

So, in this case, you have

$5^{-2}\times 5^{-1}=5^{-2-1}=5^{-3}$