How do you calculate 1812−79?

1 Answer
Becca M.
Jan 21, 2015

The answer is 1318.

Here's how to calculate it:

You'll notice that 1812 and 79 have different denominators.

In order to subtract these fractions, we need to find equivalent fractions ( i.e. fractions that are the same as our originals) that have the same denominator as one another.

To do this, let's find the least common denominator, or the smallest number that can be divided by both denominators.

One way to do this to write out the multiples of both denominators until a number repeats in the the list:

Multiples of 12: 12, 24, 36 , 48, 60
Multiples of 9: 9, 18, 27, 36

Since 36 appears in both lists, we can make both denominators 36 to create equivalent fractions.

Since 12⋅3=36, we can multiply 1812⋅33 (since 33 = 1) ...

1812⋅33=5436

And since 9⋅4=36, we can multiply 79⋅44 ...

79⋅44=2836

Now, we have equivalent fractions with a denominator of 36 and can subtract:

5436−2836=2636

And then divide the numerator and the denominator by 2 to simplify:

2636=1318

... and there's your answer!

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