Answer
Yes.
The sum of all relative frequencies is equal to 1.
Work Step by Step
$Cumulative~relative~frequency=\frac{cumulative~frequency}{sum~of~all~frequencies}$
In the last class: $cumulative~frequency~for~the~last~class=sum~of~all~frequencies$
So: $Cumulative~relative~frequency~for~the~last~class=\frac{cumulative~frequency~for~the~last~class}{sum~of~all~frequencies}=\frac{sum~of~all~frequencies}{sum~of~all~frequencies}=1$
