Question

[6.05] Your piggy bank has a total of 40 coins in it; some are dimes and some are nickels. If you have a total of $3.50, how many dimes do you have?

10

20

30

40

Answer 1

D=dimes
N=Nickels

D+N=40 (This is for the number of coins)
D*10 + N*5 = 3.50

Dimes cost 10 cents that's why i multiply 10 and Nickles cost 5 cents that's why I multiply by 5. Add them together and we have 3.50

Now solve the system of equations.

Answer 2

is the answer 10 dimes?

Answer 3

I don't know did you get 10 dimes when you solved it?

Answer 4

yes

Answer 5

What's 10*0.10=?

Answer 6

1

Answer 7

ok now you have 30 nickles left

what's 30* 0.05=?

Answer 8

1.5

Answer 9

1+1.5=?

Answer 10

2.5

Answer 11

so 10 dimes is not the answer.

Answer 12

Try solving the system of equations again

D+N=40 (This is for the number of coins)
D*0.10 + N*0.05 = 3.50

Answer 13

do i just add 0.10 + 0.05?

Answer 14

Isolate N for both equation and then substitute it to get rid of N and you are left with D and then you solve for D

For example:
D+N=40 --> N=40-D
D*0.10 + N*0.05 = 3.50 --> N = (3.50 - D*0.10) / 0.05

Now substitute:

40-D = (3.50 - D*0.10) / 0.05

Now solve for D

Answer 15

40-D=3.50-Dx0.10/0.05
-3.50 -3.50
D=36.5-Dx0.10/0.05
D=36.5-Dx0.10/0.05
D=0.10+730
D+730.1

Answer 16

http://www.wolframalpha.com/input/?i=40-D+%3D+%283.50+-+D*0.10%29+%2F+0.05++

Answer 17

Thanks Romero