Video: Subtracting a Decimal Number from a Mixed Number

Calculate (42 479/1000) − 32.79.


Video Transcript

Calculate 42 and 479 over 1000 minus 32.79.

In this question, we’re being asked to subtract a decimal from a mixed number. In order to answer the question, we’d like the two numbers to be in the same format. I’m going to convert 42 and 479 over 1000 into a decimal.

Let’s consider the fractional part of this number. 479 over 1000 means 479 divided by 1000. To divide a number by 1000, we need to move its decimal point, which in this case comes right at the end of the number, three places to the left. 479 divided by 1000 is equal to 0.479. The mixed number 42 and 479 over 1000 is therefore equal to 42.479 as a decimal.

Now we can perform our subtraction. And we’re going to do this using a column method. We must make sure that we line up the decimal points of the two numbers. The decimal point of the result will then be directly below them. So I filled in the two numbers lining up the decimal points.

For the second number, there’s a gap in the thousandths column, so I can replace this with a zero. Now I can perform the subtraction in columns starting from the right. Nine minus zero is equal to nine. Next, I try to do the subtraction of the hundredths column, seven minus nine.

I can’t do this as nine is greater than seven. So I need to borrow one from the tenths column. I now have 17 minus nine. This is equal to eight. Now I perform the subtraction in the tenths column, but again I can’t do this as seven is greater than three.

Borrowing one from the units column gives 13 subtract seven, which is equal to six. In the units column, we now have one subtract two, which we can’t do. So we need to borrow from the tens column. This gives 11 subtract two, which is equal to nine.

Finally, in the tens column, we have three subtract three which is equal to zero. And as this number is in the tens column, I don’t actually need to include it. The answer to the calculation 42 and 479 over 1000 minus 32.79 is 9.689.

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