Percentage math?

Question

Sidney spent 30% of her monthly salary on a new laptop last month. Then she spent 50% of her salary to pay her monthly bills. She put the remaining 1,200$ into her savings account. What was her monthly salary?

Answer 1

Another way to state the problem: Sidney spends 80% of her monthly salary and has $1200 left over. What is her monthly salary?

If we let x = her monthly salary then the equation that models this situation is:

x - .8x = 1200 (100% of salary, takeaway 80%, leaves 1200)

.2x = 1200 (combine similar terms)

x = 1200/.2 (divide both sides by .2)

x=6000

To verify take 30% of $6000, followed by 50% of $6000 and subtract the total spent from $6000. You should get $1200.