Adding and subtracting feet and inches can be difficult when you have two separate units you are working with. This step-by-step process should help you gain a strong understanding of how to add and subtract feet and inches, and help you to work with measurements.
Consider the information you have and what you want to achieve. Think about your initial measurement and how much you want to subtract from it. For an example, we will say the initial measurement is 12 feet and 9 inches, and we want to subtract 5 feet and 2 inches from that.
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Write out what you have as an equation. Example: 12 feet 9 inches - 5 feet 2 inches = ?
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Convert all of your values to the same unit before you subtract. So you either need to convert everything to feet or everything to inches. In this case, it's much easier to convert everything to inches. If you convert everything to feet, then you have to deal with fractions. To convert the feet to inches, simply multiply the amount of feet by 12. Example: 12 feet x 12 = 144 inches, and 5 feet x 12 = 60 inches.
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Add the inches from the foot values to the inches already known. Example: 144 inches + 9 inches = 153 inches, and 60 inches + 2 inches = 62 inches. Just to clarify: 12 feet 9 inches = 153 inches, and 5 feet 2 inches = 62 inches.
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Write out your equation again using the inch values, and subtract. Example: 153 inches - 62 inches = 91 inches.
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Leave that as an inch value or convert back to feet and inches. This is a tricky process. Divide the result by 12. Example: 91 inches / 12 = 7.58 feetWe're close, but we have a problem, we have this in feet and not inches. We know from the result (7.58) that 91 inches is 7 feet and so many inches. Figure out how many inches 7 feet is by multiplying 7 feet by 12. Example: 7 feet x 12 = 84 inches. Subtract 84 inches from 91 inches. Example: 91 inches - 84 inches = 7 inches. Now you know that 91 inches is equal to 7 feet and 7 inches.
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