Question

Sam has 18 coins in his pocket that are either quarters or nickels. The total value of these coins is $3.90.

Let q represent the number of quarters and n represent the number of nickels. The following system of equations represents this situation:

q+n=18

0.25q+0.05n=3.90

How many quarters and nickels does Sam have?

Answer 1

Substitute 18-q for n in the second equation and solve for q. Insert that value into the first equation to solve for n. Check by putting both values into the second equation.

Answer 2

idk fam

Answer 3

9
i
9
o0
0
0

Answer 4

what is ittttt I have to do my tenmarksssss

Answer 5

I too have to do my tenmarks

Answer 6

Lets first start with what is stated above~

What we know:
Q= Quarters
N= Nickels
Total amount= $3.90
Total coins=18

Q + N= Total coins (18)
0.25Q(Quarter amount) + 0.05N (Nickel amount)= $3.90 (Total amount)

Whenever you do problems like this in a systems of equations unit you MUST ALWAYS isolate only 1 letter, leaving only 1 OTHER letter behind as your new equation
Q + N = 18
-Q -Q
New Equation-
N= 18 - Q

Your next step is simple, plug and chug (don't discriminate, my teacher taught it to me that way, I remember it better in the weirdest way, as you can see)
0.25Q + 0.05(insert the N=18 - Q Equation here)= 3.90
Then simply solve for the equation.

0.25Q + 0.05(18 - Q)=3.90
0.9 - 0.05Q=3.90
Combine like terms
0.25 + 0.9 - 0.05Q=3.90
0.2Q + 0.9= 3.90
-0.9 -0.9

0.2Q/0.2 = 3/0.2
Q = 15
Now for the final step, go back to your N= 18 - Q Equation, and this time, insert your new Q

N= 18 - Q
N= 18 - (15)
N= 3
Your final results
Nickels~3
Quarters~15




This section is for the people who need this equation for homework or for another reason.


18 coins
$3.90
Q= Quarter (0.25)
N= Nickel (0.05)

Q + N = 18
-Q -Q

0.25Q + + 0.05 N =3.90

N= 18 - Q

0.25Q + 0.05(18 - Q)= 3.90

0.25Q + 0.9 - 0.05Q= 3.90
0.2Q + 0.9 = 3.90
-0.9 -0.9

0.2Q = 3
_____ _____
0.2 0.2

Q = 15




N= 18 - Q
N= 18 - (15)
N= 3