Your team lost 47 pounds at the weigh in. You know you lost 12 pounds. Your sister let it slip that she lost 1 pound more than your mother. How much did your mother lose?
if your team consisted of only you, your sister, and your mother, then your mother would have lost 17 pounds, and your sister would have lost 18 pounds.
Your mother lost 17 pounds because 47-12=35. Then I did 35 divided by 2 and got 17.5. Next I deducted what the two numbers could be. The numbers were 17 and 18. Therefore your mother lost 17 pounds.
