Question

someone what am i doing wrong?

Joe has a collection of nickels and dimes that is worth $6.10. If the number of dimes was tripled and the number of nickels was decreased by 49, the value of the coins would be $14.05. How many nickels and dimes does he have?


my answe.1X+.05y=6.1
3(.1x)+.05y-49(.05)=14.05

.3x+.05y-2.45=14.05
.3x+.05y-.2.45-2.45=14.05+2.45
.3x+.05y-.05y=16.50-.05y
.3x/.3=16.5/.3-.05y/.3
x=55+.16666667y

Answer 1

you aren't doing anything wrong.
solve the two equations.

Answer 2

plug in x into initial equation and solve for y then for x

Answer 3

yah but the last equation is endless

Answer 4

.166666666666666666666666666666666666666666666666666666666666666666666666.....

Answer 5

why dont you try elimination of variable instead of substitution.

Answer 6

how do i do that?

Answer 7

0.1X+0.05y=6.1 --------------------equation 1
0.3x+0.05y=16.50 -----------------equation 2
multiply equation 1 by 3 and subtract equation 2 from it.

Answer 8

ooo like a matrix?

Answer 9

errrrr this doesnt make sense either

Answer 10

0.1X+0.05y=6.1 --------------------equation 1
0.3x+0.05y=16.50

Answer 11

oops

Answer 12

oooo it didnt save my work

Answer 13

multiply equation 1 by 3.

Answer 14

i did

Answer 15

and post what you got.

Answer 16

i have to redo it now cause it didnt save my work to show you

Answer 17

0.3x+0.15y = 18.3 is what you get if you multiply equation 1 by 3.
so lets call
0.3x+0.15y = 18.3 ------- equation 3.

subtract equation 2 from equation 3 and post what you got.

Answer 18

-.1(.1x+.05y)=-.1(6.1)
.3x+0.05y=16.50

-.1x-.05y=-.61
.3x+.05y=16.5
-.04x=-17.11
-.04x/-.04=-17.11/-.04
x=427.75

Answer 19

this crap just doesnt make sense....

Answer 20

why did you multiply the equation by 0.1?

Answer 21

just subtract equation 1 from equation 2 and post what you got.
use by equation notations.

Answer 22

i meant use my equation notation.

Answer 23

im more confused then when i started...

Answer 24

0.1X+0.05y=6.1 --------------------equation 1
0.3x+0.05y=16.50 -----------------equation 2

subtract equation 1 from equation 2. post what you get.

Answer 25

let me do it for you.
equation 2 - equation 1
(0.3x+0.05y)-(0.1X+0.05y) = 16.50 - 6.1
make sense?

Answer 26

.2x+.1y=-10.4

Answer 27

oh wait .2x=-10.4

Answer 28

dude, you gotta work with me here. you subtracted 0.l3x - 0.1 x to get 0.2x.
why did you ADD 0.05 y and 0.05y? you subtract everything, not just the variable you like.
you do 0.05y-0.05y to get 0

Answer 29

come on man!
0.2x = +10.4, not -10.4
16.5-6.1 = 10.4
why did you get -10.4?

Answer 30

6.1-16.5

Answer 31

no, you are subtracting equation 1 FROM equation 2. that means you subtract 6.1 FROM 16.5

Answer 32

ok fine 10.4

Answer 33

right, so 0.2x = 10.4
which means x = 10.4/0.2 = 104/2 = 52

Answer 34

rather, x = 52 in equation 1

Answer 35

1(54)+.05y=6.1
54+.05y=6.1
54-54+.05y=6.1-54
.05y=-47.9

Answer 36

oops
.05y/.05=-47.9/.05
y=-958

Answer 37

0.1X+0.05y=6.1
substitute x = 52 in equation 1
you get
0.1(52) + 0.05y = 6.1
5.2+0.05y = 6.1
0.05y = 6.1-5.2
0.05y=0.9
y = 0.9/0.05
y = 90/5 = 18
how can you get y = -958?
how can you have negative nine hundred and fifty eight nickels?
think!

Answer 38

oh dear lord my calculator sucks

Answer 39

you don't need a calculator for this. you multiplied 54 by 1 instead of multiplying it by 0.1

Answer 40

0

Answer 41

0?

Answer 42

no i meant oh

Answer 43

k so plug 18 in the first or second equation?

Answer 44

no you got your answer.
you have 52 dimes and 18 nickels.

Answer 45

ohhhhhhhhhhhhhhhhhhhhhh g's im sorry for being so stupid

Answer 46

or rather, 52 nickels and 18 dimes.

Answer 47

im trying really hard to learn this stuff but it look slike chinese to me (ya know a foreign language)

Answer 48

right. you almost did it correctly.
but you have to be careful while subtracting and adding.
if you miss that you multiplied something by 1 rather than 0.1, it could lead to big problems down the road.

Answer 49

thanks for the tip....i really really appreciate your help

Answer 50

also, it helps if you put yourself in the position of the problem. suppose YOU had x amount of dimes and Y amount of nickels....... and so on. it helps you keep track of what you are trying to find, and not end up with nonsensical answers like -958. because you physically cannot have negative 900 odd nickels.

Answer 51

you are welcome. all the best!

Answer 52

thank you!