Suppose that $\int_0^1 f(t) \textrm{d}t=21$.
Calculate then $\int_0^\frac{1}{8} f(8t) \textrm{d}t$.
My work
Suppose $y=8t$, then when $t=0$ we have $y=0$ and $t=\frac{1}{8} $ implies $y=1$.
This gives $\int_{0}^\frac{1}{8} f(y) = 1$.
But I'm not sure if that correct , please help.