Question

Marie has $830 in her bank account and withdraws $60 each month. Denise has $970 in her bank account and withdraws $80 each month.
In how many months will Marie and Denise have equal amounts of money in their accounts?
A.4
B.5
C.7
D.9

Answer 1

A?

Answer 2

How did you find A?

Answer 3

I don't know.. >.<

Answer 4

In order to solve this, then I would make 2 equations for each of their amount and set then equal to each other.

Answer 5

So Marie's equation would look like this : \[y=830-60x\] Here y is the current amount and x is the amount of months.

Answer 6

And Denises equation would be: \[y=970-80x\]

Answer 7

Now you set them equal to each other and solve x: \[830-60x=970-80x <=> x=7\]

Answer 8

You can also solve this problem by graphing the two lines and noticing the point where they cross. The x-axis will be the month number, and the y-axis will be the account balance. Drop a line straight down from the point where they cross and read the value of the month off the x-axis.

Sometimes these problems are a bit trickier — for example, the exact point at which the two balances are equal may not be a "round" number of months, and the question then might ask something like "what is the first month where Marie's starting balance is greater than Denise's?"

In such a case, you could proceed in the same fashion, but you'll have to adjust your final answer accordingly. If they turned out to have an equal balance after 5.3 months, with Denise starting out with the greater balance, then the first month in which Marie's starting balance is greater would be the 6th month, not the 5th.