algebra
posted by Sarah Mae B. Oquindo on .
Money Mixtures. Elaine has $194, consisting of $20, $5, and $1 bills. The number of $1 bills is 1 less than the total number of $20 and $5 bills. If she has 39 bills in her purse, how many of each denomination does she have?

I have already solved two problems like this for you. Set up the algebraic equations that describe what you know, and solve them. There will always be as many independent equations as there are unknowns.

number of $20's  x
number of $5's  y
number of $1's  z
but z = x+y  1
x+y+z = 39
x + y + x+y1 = 39
2x + 2y = 40
x + y = 20 (#1)
also
20x + 5y + z = 194
20x + 5y + x+y1 = 194
21x + 6y = 195
7x + 2y = 65 (#2)
double #1 and subtract fron #2
5x = 25
x = 5
then in x+y = 20 , > y = 15
and finally
z = x+y1 = 19
check: is 5+15+19 = 39 ? YES
is 20(5) + 5(15) + 19 = 195 ? YEA!!