# Peter invested some money at 6% annual interest, and Martha invested some at 12%. If their combined investment was $6,000 and their combined interest was $450, how much money did Martha invest?

##### 1 Answer

Dec 12, 2016

Peter invested

Martha invested

#### Explanation:

Peter invested

Martha invested

Interest from

Interest from

Then -

#(6x)/100+(12y)/100=450#

To do away with fraction, let us multiply both sides by 100

#6x+12y=45000# ----------(1)

#x+y=6000# -----------------(2)

Let us solve the 2nd equation for

#x=6000-y#

Plug in the value of

#6(6000-y)+12y=45000#

#36000-6y+12y=45000#

#6y=45000-36000=9000#

#y=9000/6=1500#

Substitute

#x+1500=6000#

#x=6000-1500=4500#

Peter invested

Martha invested