Mary wants to buy a bicycle that costs $280. Her parents agree to pay $100. Mary will save $20 a week. write and solve an equation to find how long it will take her to save enough money.

280 = 20x + 100

20 * 9 = 180

x = 9

Check you answer:

280 = 20 (9) + 100

280 = 180 + 100

280 = 280. True statement

100+20w=280

You earn 20 per every one week (# of weeks is the variable w) you start out with 100 dollars.

To solve the equation above subtract 100 from both sides. This will leave you with 20w=180.

Then take the equation 20w=180 and divide both sides by 20 to get w=9. It will take 9 weeks for Mary to earn enough money for the bike.