System of Equations (Matrices)

[smashbrohamme]

A jar contains nickels, dimes and quarters. There are 1469 coins in the jar totaling $191.25. Assuming that the number of dimes is exactly twice that of the number of nickels, how many (each) nickels, dimes and quarters are there in the jar?We were suppose to be using matrices to solve this, it is mainly a MATLAB simulation. The idea was to get us familiar with the basics of matlab, but it seems I did a simple error and got the problem wrong. I see where my error was with the final problem solution, but I can't figure out how to correct it; or why the correction would be the reason. (If that makes any sense).

My 3 equations were
N = Nickel
D = Dime
Q = Quarter

N + D + Q = 1469
0.05N + 0.10D + 0.25Q = 191.25
N - 2D = 0 *N = 2D*

I set up a 3x3 matric
1 1 1 * N = 1469
0.05 0.10 0.25 * D = 191.25
1 -2 0 * Q = 0

My answer using Matlab was
N=640
D=320
Q=509

I attached a screenshot of the Matlab command script.

 

[axmls]

You have as your third equation that N - 2D = 0, or N = 2D, but that means that the number of nickels is twice the number of dimes. Your problem states that the number of dimes is twice that of the number of nickels.

 

[HallsofIvy]

You appear to have "1.0e3* 1.913" when you should have 191.25 (1.0e3 * 1.9125). That might be because you have Mat Lab set to round off at too low an accuracy.