From Förberedande kurs i matematik 1

When a power expression has a negative exponent, the expression's value decreases when the base increases. Thus...

\displaystyle 0.4^{-3}>0.5^{-3}

Another way to see this is to rewrite the two powers as

\displaystyle 0.5^{-3}=\frac{1}{0.5^{3}} and \displaystyle 0.4^{-3}=\frac{1}{0.4^{3}}

and because \displaystyle 0.5^{3}>0.4^{3} (see exercise a), it follows that

\displaystyle \frac{1}{0.4^{3}}>\frac{1}{0.5^{3}}

i.e. \displaystyle 0.4^{-3}>0.5^{-3}