Math Question

[vcuchic]

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Hey Guys,

This question is straight out of Top Score...
They tell me how they got to the answer, I just don't understand why at the very end we multiply 4000 by .04 opposed to .05.
Any help is greatly appreciated. Thanks

Question:
Mark has $7200 invested, part at 4% the rest at 5%. If annual income from both investments is the same, what is the income from his investment?

Answer:
$320

Explanation:
x=principle amount invested at 4%
7200-x =principle amount invested at 5%

principle x rate = income
.04x=.05(7200-x)
9x=5(7200)
x=4000
4000(.04)= income
income=160
Total income from investment is 160x2=320



Thank you!

 

[TimeforDAT]

.04x=.05(7200-x)
9x=5(7200)
x=4000
4000(.04)= income

if you plug in 4000 into the equation with the 5% interest, you get .05(7200-4000) = 160. It doesn't matter which equation you plug in x into because they are both give the same income because in the above question it was defined in the question.

 

[Resonance]

Hey Guys,

This question is straight out of Top Score...
They tell me how they got to the answer, I just don't understand why at the very end we multiply 4000 by .04 opposed to .05.
Any help is greatly appreciated. Thanks

Question:
Mark has $7200 invested, part at 4% the rest at 5%. If annual income from both investments is the same, what is the income from his investment?

Answer:
$320

Explanation:
x=principle amount invested at 4%
7200-x =principle amount invested at 5%

principle x rate = income
.04x=.05(7200-x)
9x=5(7200)
x=4000
4000(.04)= income
income=160
Total income from investment is 160x2=320



Thank you!

As the explaination states - x=principle amount invested at 4%.
These principle amounts invested have different values
y = principle amount invested at 5%
.05y = .04(7200-y)
1.25y = 7200 - y
2.25y = 7200
y = 3200
3200(.05) = 160

 

[Toothguy80]

Wow, I got this too, but it was sort of hard since you had to multiply 160 by 2 at the end for the total investment.

they should give more time for math.

 

[vcuchic]

ooh wow...
haha I def should have known that

Thanks a lot for all your help!

😀