Pre Algebra: Using Ratios to Create Proportions

1. On a map of Los Angeles, a distance of 3 miles is represented by 1.5 centimeters. If San Pedro is 24 miles from downtown Los Angeles, how many centimeters away is it on the map?

ANSWER: (B) 12

Let's solve this problem using a ratio. 3miles/1.5cm= 24miles/x cm. (xcm is what we want to know). Now let's cross multiply to find x. 3x=36. x=36/3 or x=12cm.

2. A pen factory can make 3200 pens per hour (60 minutes). At this rate, in how many minutes can the factory make 4800 pens?

ANSWER: (E) 90

Let's solve this problem using a ratio. 3200pens/60 min = 4800pens/x min. (xmin is what we want to know). Now let's cross multiply to find x. 3200x=288,000. Divide both sides by 3200. x= 90minutes. 

3. Sunny is remodeling his house. He has 3100 square feet of walls and ceilings that need to be painted. If a five gallon bucket of paint can will cover 275 square feet, how many buckets of paint does Sunny need to apply one coat to the surface?

ANSWER: (B) 12

Ratios again! $\dfrac{3100\text{ ft}^2}{x \text{ buckets}}= \dfrac{275 \text{ ft}^2}{1 \text{ bucket}}$.Cross multiply and you'll get  $3100=275x$. Divide both sides by 275 and you will get x =11.2727..... However, you cannot buy 11.2727... buckets, so you have to get 12.

4. On a large map of the East Coast, a distance of 4 miles is represented by 80 millimeters. If Baltimore is 38 miles from downtown Los Angeles, how many centimeters away is it on the map?

ANSWER: 76