Susan had a sum of money. She spent 1/5 of it in September, 1/4 of it in October, and $120 in November. After spending these amounts of money, she still had $540 left. How much money did she have at first?
Let's be accurate as possible and think first.
1200
Let X be the amount Susan had originally.

Susan spent 1 / 5 * X in September, 1 / 4 * X in October, and $120 in November.

Susan has X - 1 / 5 * X - 1 / 4 * X - $120 = $540 left.

Combining like terms, we get 11 / 20 * X - $120 = $540.

Adding $120 to both sides, we get 11 / 20 * X = $660.

Dividing both sides by 11 / 20 we get X = $1200.

.

The answer: 1200