Answer
$0.09$
Work Step by Step
We know that Coefficient of performance and efficiency are mutually related as
$COP=\frac{1}{eta}-1$
We plug in the known values to obtain:
$10=\frac{1}{\eta}-1$
$\implies \frac{1}{\eta}=10+1=11$
$\implies \eta=\frac{1}{11}$
$\eta=0.09$
