Four boards, each 12'9" in length, are laid end to end. What is their total length?

Question

nothing this comes under addition

Answer 1

This problem really boils down to unit conversion. In this case the units we are dealing with are feet and inches. In order to add two things, they need to have the same unit. Otherwise the result is incorrect / meaningless. For example 1 apple + 1 banana = 1 banapple? No it doesn't make sense!

Another way to think of it that might be more clear in steps:

 

• Convert the feet and inches to a single unit.  Either feet or inches will do, although it is usually better to first convert to inches (see engineering note below). The previous example used feet so let's use inches this time.

 

12'9'' = 12' + 9''

There are 12 inches in a foot, so we need to convert 12 feet into inches with the following relationship:

12 * 12 = 144 inches

• Add together the common units of inches

144 inches + 9 inches = 153 inches (153'')

 

• Each board is 153 inches, so we multiply times the quantity of boards we are using:

153" x 4 = 612"

 

Quick engineering note - typically professional engineers and civil engineers will prefer whole standard units instead of partial decimal units. In this case the answer is best reported as 612" or 51'. By chance this question has whole numbers in both feet and inches.  But what would happen if the original board length was 12'1/8"?

 

In our example:

If an engineer were to draw the length of a single board on an engineering drawing, it would be better to use the dimension 153" than 12.75'.  Why do you think that is?

Answer 2

Each board is 12' + 3/4' = 12.75'

 

Total length is then     4 x 12.75'