Can You Explain The Addition Of Dissimilar Fractions?

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lakeesha Hennessy Williams Profile
To add fractions that have different denominators (I assume this is what you mean by 'dissimilar fractions'), all you need to do is multiply the denominator so that the two numbers are the same.

There are a couple of rules that you'll need to stick to when doing this:

  • You need to find the lowest common denominator.
  • Whatever you do to the denominator must also be applied to the numerator.
Adding dissimilar fractions
To add two fractions that have different denominators, the first thing you'll need to do is to find a number that both of these figures can multiply into.

For example, if you're trying to add 1/5 and 3/4, then you'd look at the number that both 5 and 4 can multiply into.

Whilst there are quite a few numbers that both 5 and 4 can multiply into, 20 is the best option because it is the lowest. This is known as the 'lowest common denominator'.

The second thing to remember is that, whatever you do to the denominator of a fraction, you need to do the same thing to the numerator.

So, with 1/5 - if you are changing the 5 into 20 by multiplying it by 4, you need to do the same with the numerator (multiplying 1 by 4). This will give you 4.

The same principle applies for the second fraction. To change the denominator 4 into 20, you need to multiply by 5. This means you've got to multiply the numerators (which is 3) by 5 as well, this gives you 15.

Therefore, rather than adding 1/5+3/4, you end up adding 4/20 + 15/20. This gives you a total of 19/20, which is the correct answer!

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