I think of a number, increase it by four and double the answer. The result is 20 more than the number. Find this number.

Let’s use algebra to work this out.

Let x be the number.

I think of a number (x), increase it by 4, (x + 4) and double the answer (x + 4) x 2
the result is 20 more than the number (x + 4) x 2 = x + 20

(x + 4) x 2 = x + 20

Here can solve for x. First let’s expand the bracket.

2x + 8 = x + 20

Next, let’s take away x from both sides.

x + 8 = 20

Finally, let’s subtract 8 from both sides.

x = 12

The number is 12. :)