Lucy is sick and needs to take medicine. She will need to take 355.5 mL of medicine over three days. On the first day she will take 125.5 mL, and on the second day 120.5 mL. How much medicine does Lucy need to take on the third day?
To find out how much medicine Lucy will take on the last day, we take the total amount she will take, 355.5 mL and subtract what she has already taken on days one and two.
Since she has taken 125.5 mL and 120.5 mL she has taken a total of 246 mL.
355.5 mL – 246 mL = 109.5 mL left to take on day 3.