40$ - 100% (full price)
x$ - 70% (100-30=70%)
40 * 70 = 100x
2800 = 100x
x = 28
Answer 28$
or
40$ = 100%
then 1% = 40/100 = 0.4$
so 70% will be 0.4 * 70 = 28$
1.6m questions
2.0m answers