How I stopped an Alien Invasion using Proportion

Today the alien landed in the earth. I think one of the aliens are going to destroy the earth if we don't do a proportion question.


• A proportion is a relationship that says that two ratios or two rates are equal. A proportion can be expressed in fraction form:



60 sit-ups divide3 20 sit-ups 1 x5 5
__ = __
________ = ________ 2 x5 10
3 min divide3 1min





• You can solve proportional reasoning problems using several different methods.
A potato farmer can plant three potato plants per 0.5 m2. How many potato
plants can she plant in an area of 85 m2?

Use a unit rate. 3 plants

Use a unit rate
3 plants x2 6 plants
________ = _________
0.5m2 x2 1m2

6x85=510



Use a proportion


3 plants x170 ?
______ = ______
0.5 m2 x170 85m2

Missing value of ? is 3 × 170 = 510
The farmer can plant 510 potato plant.


Word Problem


A small gear turns 18 times in the same time that a large gear turns 4 times. How many times will the large gear turn if the small gear turns 54 times? Draw a diagram to help set up a proportion and solve the problem.





18 small gear turns x 3 54turns
_____________ = ___________
4 large gear turns x3 ? turns



The aliens didn't kill us. Good thing the end.