Question

ana completed 40 percent of her homework assignment.her assignment contains 30 math problems.how many problems does ana still need to complete

Answer 1

$30*0.4=12 \\ \\ 30-12=18$

Since 12 is 40% of 30, she has already completed 12 problems. Subtract that from 30, and you can find that she still needs to do 18 problems.

Using Proportions:

$\frac{40}{100} = \frac{x}{30} \\ \\ 100x=1200 \\ \\ x=12 \\ \\ 30-12=18$