The average adult is about 60% water. One liter of water has a mass of 1 kilogram. If a person’s body contains 45 liters of water, what is the person’s mass in kilograms?

Question

Write the percent as a ratio with a whole of 100. Then find an equivalent ratio with the liters as the part.

The number of liters is equal to 60% of the total mass.

Answer 1

The average adult is about 60% water. One liter of water has a mass of 1 kilogram. If a person’s body contains 45 liters of water, what is the person’s mass in kilograms?

Write the percent as a ratio with a whole of 100. Then find an equivalent ratio with the liters as the part.

The number of liters is equal to 60% of the total mass.

water mass 60

_______________ = _______

total body mass 100

1 liter 45 liters

__________ = ______________

1 kilogram 45 kilograms

water mass 60 45 kilograms

______________ = ________ = ___________________

total body mass 100 total body mass (kg)

Calculate the total body mass, using cross multiplication. First, I will reduce 60/100 to 3/5.

60 3 45

____ = _____ = _____

100 5 T

(5)(45) = 3T

225 = 3T

75 = T

The body's total body mass is 75 kilograms.

60% as a ratio can be written as 60:100. Some write their ratios as fractions, such as 60/100.

The ratio of water to total body mass is 45:75 or, if you prefer, 45/75.