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Arithmetic Grade Six

Lesson Thirty-one: Subtracting Feet and Inches

Sometimes it is necessary to regroup when subtracting. In this case the inches column borrows from the feet column like in this problem:


	   3 ft, 7 in
	-  1 ft, 8 in
	--------------

Before we can do this problem we must regroup. Since 1 foot equals 12 inches we can rewrite the problem like this:


	   2 ft, 19 in
	-  1 ft,  8 in
	--------------

We converted one foot to twelve inches and added these inches to the 7 that were already in the inches column. Now all we have to do is subtract each column.


	   2 ft, 19 in
	-  1 ft,  8 in
	--------------
	   1 ft, 11 in

Here's another example:


	   5 ft,  2 in
	+  2 ft, 11 in
	--------------

After borrowing one foot we rewrite the problem like this:


	   4 ft, 14 in
	+  2 ft, 11 in
	--------------

Now solving the problem is easy:


	   4 ft, 14 in
	+  2 ft, 11 in
	--------------
	   2 ft,  3 in

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