Walt made an extra $12,000 last year from a part-time job. He invested part of the money at 7% and the rest at 9%. He made a total of $970 in interest. How much invested at 7%?
I think the answer is $840 but I am not positive this is correct. Please help.

Jane invested some amount at the rate of 12% simple interest and some other amount at the rate of 10% simple interest. She recieves yearly interest of $130.00. Randy also invested in the same scheme, but he interchanged the amounts invested and recieved $4.00 more as interest. How much amount did each of the invest at different

I would like to know if I am on the right track to writin this as a "systems of equations" using the substitution process. How much further do I have to go if this is right so far?
A family made an investment for 1 year that earned $7.50 simple interest. If the principal had been $25 more and the interest rate 1% less, the in

1. Joe has a collection of nickels and dimes that is worth $5.65. If the number of dimes was doubled and the number of nickels was increased by 8, the value of the coins would be $10.45. How many dimes does he have?
2. An express train and a local train leave GraysLake at 3 P.M. and head for Chicago 50 miles away. The express

Problem 1. Investments. William opened two investment accounts for his grandson's college fund. The first year, these investments, which totaled $18,000, yielded $831 in simple interest. Part of the money was invested at 5.5% and the rest at 4%. How much was invested at each rate?
Problem 2.
"Arctic Antifreeze" is

What computer applications can be used to graph systems of equations? Have you ever personally used any applications to graph an equation? In what circumstances does it make more sense to graph a system than to use the substitution, elimination, or matrix methods?

This posting addresses the following questions:
What does the concept "time value of money" mean? Why is the concept important? What are some practical applications of this concept for businesses? For individuals? What assumptions have to be accepted when discussing the "time value of money"?

There are many applications used in the area of solving systems of equations. For example, systems of equations can be used to find the optimal number of items to produce to ensure the highest profit of those particular items. Systems of equations can be solved by four methods: graphing, substitution, elimination or with matrice

1. Emily Harrington made two investments for one year totaling $7,000. The interestrates were 4% and 7%. If she received $415 in interest, how much money was invested at each rate?
at 4%
at 7%
2. Two lengths of wire total 132 fest. One length is 42 feet longer than the other. How long is each length of the wire?
And
3.