In ten years, I'll be twice my brother's age. The sum of our ages will then be 45 years old. How old am I now?
Let's think step by step.
20
Let X be my age now.

In ten years, I'll be X + 10 years old.

In ten years, my brother will be (X + 10) * 1 / 2 years old.

In ten years, (X + 10) + (X + 10) * 1 / 2 = 45.

So (X + 10) * 3 / 2 = 45.

X + 10 = 45 * 2 / 3 = 30.

X = 30 - 10 = 20 years old.

.

Therefore, the answer is 20