1) Twelve hungry teenagers can devour a very large pizza in 20 minutes. How many teenagers would it take to finish a very large pizza in 15 minutes? (Assume that all teenagers eat pizza at the same rate.)
2) For a statue of Miss Levans, the amount of gold required is proportional to the square of the height of the statue. A statue of Miss Levans that is 20 feet tall requires 80 pounds of gold. How many pounds of gold does a statue that is 25 feet tall require?
3) Tina lives 30 miles away from her work, and she normally drives at 45 miles per hour. If she wants to get to work 10 minutes earlier, how fast should she drive to work, in miles per hour?
For number 1, we can use what I call the "see-saw" principle
12 * 20 = N * 15 divide both sides by 15
12 * 20 / 15 = N = 240 / 15 = 16 is the number needed
Here's number two
P = k H^2 where P is the pounds of gold needrd..k is the proportionality constant and H is the height...we need to find "k"
80 = k * 20^2
80 = k * 400 divide both sides by 400
1/5 = k
So..one that is 25 feet tall requires
P = (1/5) * 25^2 = (1/5) * 625 = 125 pounds
Here's the last one
It takes Tina 30miles / 45mph = 2/3 of an hour to get to work = 40 minutes
So......10 minutes earlier is 30 minutes.....so........to travel 30 miles in 30 minutes....she must travel at 1 mile per minute = 60 mph