Nine added to 3/7 of a number yield 42

Answer 1

When you see "of a number" what it actually means is a variable, like X or Y.

So let's write this out as an equation:

3/7X + 9 = 42

Now here's something no math teacher ever taught me, but the reason an equation is called an equation is because everything on both sides of the "=" sign equate to the same thing. What the exercise wants you to do is prove that, so let's perform the same operations to the right side as we have on the left side, but in reverse.

Subtract 9 from 42 instead of adding it.

3/7X = 33

Now here's where it's a little tricky, X is being multiplied by 3/7, so what's the reverse of that? Multiplying by 7/3. So multiply 33 by 7/3. We do this by multiplying 33 by the numerator then dividing by the denominator:

33*7/3 = 231/3 = 77

So the answer is 77!

You can verify this by performing these operations in reverse. Multiply 77 by 3/7 then add 9, which gives you 42.