## Thursday, October 13, 2011

### Sarah's Proportion Post

Ratio - a comparison of two quantities that have the same unit of.

Suppose that you have a bag of 20 marbles. You pour 5 marbles into your hand. The ratio of marbles in your hand to the total number of marbles is 5 to 20, or 5:20, or 5/20.

Rate - A comparison of two quantities that have different units of measure.

The rate at which you type may be 50 words per minute. The rate at which your parents' car travels may be 55 miles per hour.

Proportion - An equation which states that two ratios are equal.

Proportions can be used to predict information, such as: "a baseball player has a batting average of 50 hits in 100 at-bats. How many hits will she have in at-bats?"

1) 5 hours to travel 360 miles is about _____mph.
• 5 hours to travel 360 miles is about 72 miles mph.

2) As a playgroup worker, if I increase the amount of apple juice I am serving at the playgroup from 25 ml to 100 ml, how much should I increase the the orange juice to, to keep the quantities in the same proportion? The orange juice is 50 ml to start with.
• apple/orange 25/100 = 50/200