  SAT book pg.374 #7

<p>One adult and 10 children are in an elevator. if the adult's weight is 4 times the average weight of the children, hen the adult's weight is what fraction of the total weight of the 11 people in in the elevator?</p>

<p>the answer is 2/7 -I have no idea how to do it</p>

<p>Make the weight of 1 child 1 unit. The adult is therefore 4 units in weight. There are 10 children, so there are 10 units of child weight in the elevator. There is 1 adult, so there are 4 units of adult weight in the elevator. The total weight of humans in the elevator is the sum of the adult weight and the child weight. 10+4=14. The adult weight is 4/14 the total human weight, or 2/7.</p>

<p>That’s clever, Cosmological. I said each child weighs 50lbs, making the total weight of the children 500lbs and the avg weight of the children 50lbs. The adult’s weight is 4x the avg weight of the children, so the adult weighs 200lbs. The ratio of the adults weight to the total weight of everyone in the elevator is 200/700, or 2/7.</p>

<p>Yes, both solutions are correct. It’s usually simpler to assume that each child weighs 1.</p>