Question

explain how to mentally calculate the sale price of a $30 sweater that is on sale for 40 % off.

Answer 1

Find 40% of 30 in your head, then subtract that amount from 30 dollars

Answer 2

By the way, 10% of any number is one decimal place to the left.

So 10% of 30 is 3

If you multiply 10% times 4 you get 40%
If you multiply 3 times 4 , you get 12

Now, you do all of that in your head.

Now, that you have 40% of 30, the last step of this mental math problem is to subtract 30 - 12 to get 18.

Therefore the discount price of the sweater is 18 dollars.

Answer 3

The reason you subtract 12 from 30 is because that's what 40% discount means.
40% discount means to take 40% of the original amount, and subtract it from the original amount.