Proportions

Question

Niu earned $312 on an investment of $800. How much would $1100 have earned in the same investment?

Answer 1

Basically we are saying she invested $800 and earned $312 and we

want to know how much she would have made had she invested $1100.

 

Our proportion reads as:

800 is to 312 as 1100 is to x

 

You set that up as two equal fractions

800/312 = 1100/x

 

Cross multiply

 

800x = 1100(312)

x = 1100(312)/800

x = $429

 

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Another way to set this up is to check the factor by

which the initial investment was raised and multiply the

earnings by the same amount.

 

800x = 1100

x = 11/8 = 1.375

 

We multiplied our investment by 1.375 so if we

multiply our original earnings by the same amount

we should find out how much she would have earned.

 

312(1.375) = $429

 

As can be seen, both methods yield the same answer.

 

Hope this helps.