# Another investment question

• Jan 13th 2009, 05:39 PM
asugirl87
Another investment question
Susan places \$4900 in three investments at rates of 9%, 10.8% and 16.2% per annum, respectively. The total income after one year is \$ 640.80 . If the amount placed in the third investment is \$900 more than the amount placed in the second, find the amount of each investment.

and also...

The admission fee at an amusement park is \$ 1.50 for children and \$ 4.00 for adults. On a certain day, 291 people entered the park, and the admission fees collected totaled \$824 . How many children and how many adults were admitted?
• Jan 13th 2009, 05:45 PM
Quote:

Originally Posted by asugirl87
Susan places \$4900 in three investments at rates of 9%, 10.8% and 16.2% per annum, respectively. The total income after one year is \$ 640.80 . If the amount placed in the third investment is \$900 more than the amount placed in the second, find the amount of each investment.

I will help you on the construction on this problem only so that you will have a chance to learn on your own. Working problems like this by yourself is important to the understanding of problem solving.

So we have three investments, lets say
x is the investment for the rate of 9%
y is the investment for the rate of 10.8%
z is the investment for the rate of 16.2%

Since Susan invests \$4900 we know that

1) x + y + z = 4900

Since the total interest of that year is 640.80, we also know that the sum of the generated interest from each investment totals this number. So

2) .09x + .108y + .162z = 640.80

Since we know the amount placed in the third investment is \$900 more than the amount placed in the second (I'll assume respectively from lower to higher interest rate), then

3) y = z + 900

Using 1,2,3 solve for the system of linear equations.