Question

Randomly grabbing 22 coins from a pile of quarters and dimes, my brother Marshall counts out $3.70 in change. Find how many quarters and dimes he has.

Answer 1

I go the answer in geogebra, but I cant find it on paper. Help @Hero ?

Answer 2

Im pretty sure I need to use a system.

Answer 3

Let x = number of quarters
Let y = number of dimes:

Then
The Total number of coins is represented by:
x + y = 22

The Total amount of money in dollars is represented by:
.25x + .10y = 3.70

Find the values of x and y.

Answer 4

Thats what I have.

Answer 5

And let me guess, you can't figure out the rest of it.

Answer 6

I use substitution, but only get .24x = 1.5 everytime.

Answer 7

I believe me, I knocked out past questions easy peasy.

Answer 8

typing fail

Answer 9

Why don't you try multiplying the first equation by .25?

Answer 10

Use elimination?

Answer 11

Then afterwards, subtract the second equation from the first.
Yeah, it'll be easier for you

Answer 12

Can't you figure it out using substitution?

Answer 13

@Dahmanman, please do as I ask.

Answer 14

I'll try it though

Answer 15

You could do it either way, if you knew how, but apparently you don't.

Answer 16

so lets see, -.25x - .25y = -5.5

Answer 17

You are not doing as I ask. I specifically said what to do.

Answer 18

I see now why you don't know how to do certain things.

Answer 19

Im using elimination!
What else did you ask?

Answer 20

Should I repeat it?

Answer 21

Yes, please.

Answer 22

Really? Because I already posted what to do. I never mentioned to "use elimination".

Answer 23

I posted a specific set of instructions.

Answer 24

It was quite simple indeed.

Answer 25

You have no idea what elimination is?

Answer 26

I do, but I asked you to multiply the first equation by .25. Then afterwards subtract the second equation from the first.

Answer 27

alright, I get .24y = 1.8

Answer 28

Okay, so you know what to do from there.

Answer 29

1.8/.24 = 7.5

Answer 30

The reason I wanted you to do it my way is for a couple reasons:

1. To avoid dealing with negative numbers
2. To mimimize error.

Your division is incorrect sadly. Your mistakes are mental.

Answer 31

Hmm.. I don't know why im having so much trouble with this one problem

Answer 32

@dahmanman how'd you get .24y = 1.8 ?

0.25x + 0.25y = 5.5
0.25x + 0.10y = 3.70

When you subtract the second from the first, you shouldn't get 0.24y = 1.8.

Answer 33

Oh, wait a minute. its .15y = 1.8

Answer 34

which equals 12 = y

Answer 35

Very good

Answer 36

I was confusing tenths with hundredths! I cant believe I made such a stupid mistake. Thanks for your time, guys!

Answer 37

I'm just happy I didn't have to give you the answer. Sadly, you may be the first student who actually was able to figure out the solution with me only needing to post a hint. Most other students are completely clueless afterwards.

Answer 38

My only gripe is, I hope now you understand not to make assumptions when people are suggesting solution steps.

Answer 39

Do exactly as instructed, especially with math.

Answer 40

I did notice we subtracted the equations instead of multiplying the first by -.25. I wasn't taught to use that way in my lesson, so I was confused. thats a much easier way instead of writing down a bunch of negative signs

Answer 41

Precisely

Answer 42

Thanks again, guys!

Answer 43

One reason is, we're dealing with money and you should never end up with negative money. In this case -$5.50 doesn't really make sense because there's no such thing as negative money.

Answer 44

Maybe you could argue that you're subtracting the $5.50, but there's no way to justify multiply by a negative quarter.