# Thread: Original Principle, different rates/investment

1. ## Original Principle, different rates/investment

Linus and Macy put the same amount of money into different investments for one year. Linus' investments increased by 8%. Macy's investments decreased by 7%. The difference in the value of their investments was \$750 after the one year. What was the original amount of money that each invested?
How do I start to solve this?
Do I just substitute the known values into I=PRT and solve for P, or is there a different equation that is meant to be used.

2. Hint:
a = amount invested
a@8% - a@-7% = 750
a(1 + .08) - a(1 - .07) = 750
Solve for a

3. Originally Posted by Denis
Hint:
a = amount invested
a@8% - a@-7% = 750
a(1 + .08) - a(1 - .07) = 750
Solve for a
a(1 + 0.08) - a(1 -0.07) = 750
a(1.08) - a(0.93) = 750
1.08 - 0.93 = 0.15
0.15 * a = 0.15a
750/0.15 = a
a = 5000
This is correct right?

4. Originally Posted by SaltyPoro
a(1 + 0.08) - a(1 -0.07) = 750
a(1.08) - a(0.93) = 750
1.08 - 0.93 = 0.15
0.15 * a = 0.15a
750/0.15 = a
a = 5000
This is correct right?
YESSSSSSSSS!
You can check if correct:
5000 * .08 = 400
5000 * -.07 = -350
400 - (-350) = 750 ; OK?

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