Question

Susan is creating a solution. A formula for the solution calls for 7/10 mL of water. Susan wants to make 2/7 less of the solution than the formula creates.

How much water should Susan use?
Express your answer as a fraction in simplest form.

Answer 1

Susan wants 2/7 less of the solution. The whole solution is equivalent to 1. So she wants the amount: 1 - 2/7 = 5/7 mL.
She takes 5/7 mL of 7/10 mL.
Therefore (5/7)*(7/10) = 35/70 = 1/2 mL

Answer 2

7|10 - 2|7 is the answer because she needs to use 7/10 but she wants to make 2/7 less so you subtract 2/7 from 7/10 and that's the answer