She has 38 nickels
N as the number of nickels, D as the number of dimes, and Q as the number of quarters.
She has 140 coins in total, so we can writen:
N + D + Q = 140.
And the total value is $19.00
Then we have:
N*0.05 + D*0.10 + Q*0.25 = 19
And "The difference in the number of dimes and the number of quarters is 10."
D - Q = 10.
So we have a system of 3 equations and 3 variables:
N + D + Q = 140
N*0.05 + D*0.10 + Q*0.25 = 19
D - Q = 10.
First, let's isolate one of the variables in the third equation, i will isolate D.
D = 10 + Q.
Now we can replace this in the other two equations:
N + (10 + Q) + Q = 140
N*0.05 + (10 + Q)*0.10 + Q*0.25 = 19.
Now we can isolate Q in the first equation:
N + 10 + 2*Q = 140
2*Q = 140 - 10 - N
Q = 130/2 - N/2. = 65 - N/2
Now we can replace this in the other equation:
N*0.05 + 10*0.10 + Q*(0.10 + 0.25) = 19
N*0.05 + 10*0.10 + (65 - N/2)*( 0.35) = 19
Now we can find the number of nickels.
N*0.05 + 1 + 22.75 - N*0.175 = 19
23.75 - N*(0.175 - 0.05) = 19
23.75 - 19 = N*0.125
4.75/0.125 = N
38 = N
She has 38 nickels
To learn more about matrices from the given link
brainly.com/question/17537269
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