Expert: Richard J. Raridon - 11/25/2007

Question
Hey i have a few questions that i do NOT understand can U please help me??

1. Laura has a total of 16 coins: quarters, dimes, and nickles. the total value of her money is $1.80. the number of nickels is the sum of the number of dimes and quarters. How many of each coin does she have? I have no idea how to set this up as a matrix.

2. Marina has $24,500 to invest. she divided the money into different accounts. At the end of the year she has made $1300 in interest. the yield on each of the three accounts was 4%, 5.5%,and 6%. if the amount of money in the 4% account was four times the amount of money in the 5.5% account , how much money has she placed in each account?
How do i set this up in matrix and solve it?

Thank you sooo much

Answer
1. Q+D+N = 16 and N + Q+D and 0.25Q+0.10D+0.05N = 1.80
Substitute for N in each equation and you have two equations, two unknowns.
2. let x = amt. invested at 4%, y = amt. at 5.5% and z = amt. at 6%.  
then x+y+z = 24500, x=4y and 0.04x+0.055y+0.06z = 1300
substitute for x in each eq. and you have two equations, two unknowns.