Question

Keisha has a collection of dimes and nickels worth a total of $4. If she has 50 coins in all, how many nickels does Keisha have?

Answer 1

30 dimes+20 nickels

30x10=300

20x5=100

total 400 cents= $4

Answer 2

Nickels (n): $0.05
Dimes (d): $0.10

Set up a system of equations
Cost/Worth: .05n + .10d = 4.00
Quantity: n + d = 50

Use elimination or substitution to solve.
I am using the elimination method:

100(.05n + .10d = 4.00) → 5n + 10d = 400
-10( n + d = 50 ) → -10n - 10d = -500
-5n = -100
n = 20

Plug that into one of the original equations to solve for "d"
n + d = 50
(20) + d = 50
d = 30

Answer: there are 20 nickels and 30 dimes.