SOLUTION: Kayanna decided to save the 5-cent, 10-cent, and 25-cent pieces she collected after purchase made while shopping with her father. After a period of days she had a total of 246 coin

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Question 1100689: Kayanna decided to save the 5-cent, 10-cent, and 25-cent pieces she collected after purchase made while shopping with her father. After a period of days she had a total of 246 coins. The money value of the coins was $25.50. If the amount of 5-cent pieces was 40 less than twice the amount of 10-cent pieces.
a. Derive a system of three equations showing the information given.
b. Use Cramer's Rule to find how many of each type of coins she had.

Please assist
Answer by richwmiller(17219) About Me  (Show Source):
You can put this solution on YOUR website!
f+d+t=246
.05f+.10d+.25t=25.50
f=2*d-40
f-2*d+0*t=-40
f+d+t=246
.05f+.10d+.25t=25.50
1,-2,0,-40
1,1,1,246
.05, .10,.25,25.50
f=120 nickels, d=80 dimes, and t=46 quarters
Solved by pluggable solver: Using Cramer's Rule to Solve Systems with 3 variables







First let A=%28matrix%283%2C3%2C1%2C1%2C1%2C.05%2C.10%2C.25%2C1%2C-2%2C0%29%29. This is the matrix formed by the coefficients of the given system of equations.


Take note that the right hand values of the system are 246, 25.5, and -40 and they are highlighted here:




These values are important as they will be used to replace the columns of the matrix A.




Now let's calculate the the determinant of the matrix A to get abs%28A%29=0.55. To save space, I'm not showing the calculations for the determinant. However, if you need help with calculating the determinant of the matrix A, check out this solver.



Notation note: abs%28A%29 denotes the determinant of the matrix A.



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Now replace the first column of A (that corresponds to the variable 'x') with the values that form the right hand side of the system of equations. We will denote this new matrix A%5Bx%5D (since we're replacing the 'x' column so to speak).






Now compute the determinant of A%5Bx%5D to get abs%28A%5Bx%5D%29=66. Again, as a space saver, I didn't include the calculations of the determinant. Check out this solver to see how to find this determinant.



To find the first solution, simply divide the determinant of A%5Bx%5D by the determinant of A to get: x=%28abs%28A%5Bx%5D%29%29%2F%28abs%28A%29%29=%2866%29%2F%280.55%29=120



So the first solution is x=120




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We'll follow the same basic idea to find the other two solutions. Let's reset by letting A=%28matrix%283%2C3%2C1%2C1%2C1%2C.05%2C.10%2C.25%2C1%2C-2%2C0%29%29 again (this is the coefficient matrix).




Now replace the second column of A (that corresponds to the variable 'y') with the values that form the right hand side of the system of equations. We will denote this new matrix A%5By%5D (since we're replacing the 'y' column in a way).






Now compute the determinant of A%5By%5D to get abs%28A%5By%5D%29=44.



To find the second solution, divide the determinant of A%5By%5D by the determinant of A to get: y=%28abs%28A%5By%5D%29%29%2F%28abs%28A%29%29=%2844%29%2F%280.55%29=80



So the second solution is y=80




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Let's reset again by letting A=%28matrix%283%2C3%2C1%2C1%2C1%2C.05%2C.10%2C.25%2C1%2C-2%2C0%29%29 which is the coefficient matrix.



Replace the third column of A (that corresponds to the variable 'z') with the values that form the right hand side of the system of equations. We will denote this new matrix A%5Bz%5D






Now compute the determinant of A%5Bz%5D to get abs%28A%5Bz%5D%29=25.3.



To find the third solution, divide the determinant of A%5Bz%5D by the determinant of A to get: z=%28abs%28A%5Bz%5D%29%29%2F%28abs%28A%29%29=%2825.3%29%2F%280.55%29=46



So the third solution is z=46




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Final Answer:




So the three solutions are x=120, y=80, and z=46 giving the ordered triple (120, 80, 46)




Note: there is a lot of work that is hidden in finding the determinants. Take a look at this 3x3 Determinant Solver to see how to get each determinant.