Expert: Josh - 3/20/2008

Question
I don't understand how to solve this: Add 12 1/3tons to 20 tons 500 pounds???

Answer
Evangeline,

We cannot add quantities with different units. Consider writing down 1 unit. What does the "1" really mean? This is clearly ambiguous, as we are not sure whether the "1" is relative to one tonne or one pound.

We need to express everything in terms of the same unit before we can add them together. If we decide to use "tonne" as our unit of measure, then we need to know the relationship between tonne and pound.

Fact: 1 tonne = 1000 kilograms (kg)

Go to http://www.digitaldutch.com/unitconverter/
Look up "Mass" and convert "kilogram" into "pounds" (lb)

Outcome: 1 kg = 2.204623 lb

Question: How many kilograms is in 500 pounds? Let the answer be X.
We set this up as  1/2.204623 [kg/lb] = X/500 [kg/lb]
Multiplying both sides by 500, we get X = 500/2.204623 kg.
(Use a calculator to simplify this).

Since 1 kg = 1/1000 tonne, X corresponds to (500/2.204623/1000) tonne.

Now, 20 tonne and 500 pounds equal 20 + 1/(2x2.204623) [tonne]
We can now add this directly to 12.333333...[tonne] to obtain the final answer.

Please try this yourself.

Good luck