Question

A $52 sweater is on sale for $31.20 what is the sales percent

Answer 1

Use the percent proportion: 
$\frac{a}{b} = \frac{p}{100}$
a = part = $31.20
b = base = $52
p = percent = what we need to find out
100 = x out of 100 (100 is the total percent)
so, our proportion looks like:
$\frac{31.20}{52.00} = \frac{p}{100}$
To solve, use cross products.
31.20 x 100 = 3120
p x 52.00 = 3120 (cross products are always equal)
To solve for p, divide 3120 by 52 and you get 60.
The answer is 60%