What is the mass in kg of a person who weighs 185 pounds?

##"185 lb"~~"84.2 kg"##

This question can be answered by using dimensional analysis.

The relationship between kilograms and pounds is ##"1 kg=2.20 lb"##.

This gives us two conversation factors:

##"1 kg"/"2.20 lb"## and ##"2.20 lb"/"1 kg"##

Multiply the given dimension ##("185 lb")## by the conversion factor with the desired unit in the numerator. This will cancel the unit we wish to convert.

##185" lb"xx(1" kg")/(2.20" lb")="84.2 kg"## rounded to three significant figures.