Question

sarah has $400 in her saving account and she has to pay $15 each month to her parents for her cell phone. draius has $50 and he saves $20 each month from his job walking dogs for his neighbor. at this rate, when will sarah and darius have the same amount of money? how much money will they each have?

Answer 1

For this question, personally, I would do it algebraically.

So set m to the number of months until they will have the same amount of money. Then you can write an equation matching this scenario, and solve for m as well.

So first, write the side of the equation for Sarah.

She originally had $400, and each month pays $15.

So 400 - 15m for subtracting how much she pays in total, 15m, from her total amount of money, $400.

Now, write the side of the equation for Draius. 

He originally had $50, and he gets $20 each month.

So the equation would be 50 + 20m, for how much he gets in total adding to $50.

Now set the two equal.

400 - 15m = 50 + 20m

Now, move all like terms to opposite sides by using opposite operations.

Subtract 50 from both sides:

400 - 50 - 15m = 50 - 50 + 20m
350 - 15m = 20m

Now add 15m to both sides.

350 - 15m + 15m = 20m + 15m

350 = 35m

Divide both sides by 35:

350/35 = 35m/35

m = 10

So Sarah and Darius will have the same amount of money in 10 months.

Now you can plug 10 into the equation to find out how much money they both have.

I'll just plug it in for 400 - 15m:

400 - 15 (10)
= 400 - 150
= 250

And since they'll both have the same amount of money, they'll both have $250.