Give to the number the letter x, then the 40% of x is 8:
[tex]x\cdot\frac{40}{100}=8[/tex]Solve the equation for x:
Multiply both sides of the equation by 100:
[tex]\begin{gathered} x\cdot\frac{40}{100}\cdot100=8\cdot100 \\ \\ x\cdot40=800 \end{gathered}[/tex]Divide both sides of the equations into 40:
[tex]\begin{gathered} x\cdot\frac{40}{40}=\frac{800}{40} \\ \\ x=20 \end{gathered}[/tex]Then, 8 is the 40% of 20