there were 80 gallons of gas in a tank...

Question

There were 80 gallons of gas in a tank. Now there are only 50 gallons left. 

a) calculate the decrease in the amount of gas in the tank as a percentage of the original. This percentage is the percent decrease in the amount of gas in the tank. 

b) Now calculate the new amount of gas in the tank as a percentage of the original, and subtract it from 100%

c) With the aid of a simple picture, explain why part b) must also produce the percent decrease that you calculated in a)

Answer 1

(a)

 

Set up a proportion:

 

80 gallons → 100%

50 gallons → x

 

x = 50*100 / 80 = 62.5% left; the decrease is 100% - 62.5% = 37.5%

 

(b)

 

Multiply the original 80 gallons by the decimal form of 62.5%, which is 0.625:

 

0.625*80 = 50 gallons left

 

The decrease is 80 - 50 = 30 gallons

 

Set up a proportion:

 

30 gallons → 80 gallons

x → 100%

 

x = 30*100 / 80 = 37.5%

 

The reduction is 37.5%, which is the same as 100% - 62.5%.

 

(c) Unable to draw pictures in this format.