320 is 80% of 400.
Step 1: Translate the words into an equation.
320 | is | what percent | of | 400 |
320 | = | x | $ \cdot $ | 400 |
Step 2: Solve for $ x $.
$$ \begin{aligned} 320 &= x \cdot 400 \\[1.2 em] 400 \cdot x &= 320 \\[1.2 em] x &= \dfrac{ 320 }{ 400 } \\[1.2 em] x &= 0.8 \end{aligned} $$Step 3: Express $ x $ as a percentage.
$$ x = 0.8 = 0.8 ~~\cdot~~ 100 \% = 80 \% $$