Think of it this way... if we have two fractions:

then we can add them by getting a common denominator. The common denominator in this case will be 4 x 5 = 20. So we need to multiply the fraction on the right to put it in the form (something)/20.

Now, we can't change the value of 1/5, but we must find a way to multiply the denominator by a factor of 4. How can we do this? Well if we multiply the fraction 1/5 by 1, then we still have 1/5. So I'm going to choose a particular kind of form of 1 to multiply the 1/5 by.

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We do the same thing with 3/4, but in this case we need to multiply the denominator by 5, thus

Why do we do all this? In order to add two fractions we need to have a common denominator, in this case 20.

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The problem you are being asked to do is very similar, except in this case I'm going to change the 1 into 1/1, so we can have the number 1 in fractional form. So how do you add