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On monday, Tanya counted the number of 10-cent coins, 20-cent coins and 50-cent coins in her piggy bank. The number of 10-cent coins was 24 more than the number of 50-cent coins. On tuesday, Tanya spent 3 over

5 of the 10-cent coins, 1 over 4 of the 20-cent coins and 18 50-cent coins. Tanya then found that she had an equal number of 10-cent coins and 20-cent coins. The number of 50-cent coin now formed 40% of all the coins she had left.

(a)Tanya had how many 10-cent coins at first?

(b)How much money did Tanya spent in all?

Guest Apr 30, 2015

Best Answer 

 #6
avatar+78618 
+10

Addendum......I believe I spotted Melody's error

She has

0.72X  -  16.8 =X  - 42

16.8 + 42  =  x - 0.72X

 

But the 16.8 should be negative

So....it should be....

-16.8 + 42  = 0.28X

25.2  = 0.28X

X = 90  = the number of 10 cent coins, originally.....

And our answers would now agree....

Hey.....no biggie......!!!!

 

  

CPhill  May 2, 2015
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7+0 Answers

 #1
avatar+91001 
+5

On monday, Tanya counted the number of 10-cent coins, 20-cent coins and 50-cent coins in her piggy bank. The number of 10-cent coins was 24 more than the number of 50-cent coins. On tuesday, Tanya spent 3 over

5 of the 10-cent coins, 1 over 4 of the 20-cent coins and 18 50-cent coins. Tanya then found that she had an equal number of 10-cent coins and 20-cent coins. The number of 50-cent coin now formed 40% of all the coins she had left.

(a)Tanya had how many 10-cent coins at first?

 

 

This one is really confusing is it not :)

Let the number of tens be X, the number of twenties be Y and the number of fifties be Z

Z+24=X

X-24=Z

-----

now after her spending spree this is what what she has left

(2/5)X+(3/4)y+(Z-18)   coins

and

(2/5)X=(3/4)Y

so Y = 0.4X/0.75 = (8/15)X      and from before       X-24=Z

also

0.4((2/5)X+(3/4)y+(Z-18) )=Z-18

The first thing we want is X so I will get all this in terms of X and solve and hopefully the answer is a whole number. :)

0.4((2*(2/5)X+(X-24-18))=X-24-18

0.4((0.8X+(X-42))=X-42

0.4(1.8X-42)=X-42

0.4*1.8X   -   0.4*42=X-42

0.72X  -  16.8 =X  - 42

 -16.8+42 =X  - 0.72X

25.2=0.28X

X=90

so there was originally 90 ten cent peices

 

(b)How much money did Tanya spent in all?

X=90

Y=(8/15)X = 8/15*9048

She spent    (3/5)*X = (3/5)*90 = 54 ten cent coins = $5.40

She spent    (1/4)*Y = 0.25*48 = 12 twenty cent coins = $2.40

She spent   18 fifty cent coins  =  $9

 

Total spent = 5.40+2.40+9= $16.80

 

I fixed this after CPhill told me, by Private message,  of a careless error.    Thanks Chris 

I only just realized that he has posted a proper answer underneath then whited it out.

You don't need to do that Chris - I shall unwhite it.  It is a good answer :)

Melody  Apr 30, 2015
 #3
avatar+78618 
+10

I get a different answer from Melody on this one.....

 

Let x  be the number of 50 cent coins in the beginning

Let y be the number of 20 cent coins in the beginning

Let x + 24 be the number of 10 cent coins in the beginning

 

And after the spree we have

x - 18   = the number of 50 cent coins

(2/5)(x + 24) = the number of 10 cent coins = the number of 20 cent coins

 

So the total coins left after the spree = 2(2/5)(x + 24) + ( x -18)  = (4/5)(x + 24) + (x - 18)

And 40% of these = the number of 50 cent coins left   ....  so we have

.40[ (4/5)(x + 24) + (x - 18) ] = (x - 18)

(2/5)[ (4/5 (x + 24) + (x - 18) ] = (x - 18)

[ (4/5 (x + 24) + (x - 18) ]  = (5/2)(x - 18)   multiply through by 10

8(x + 24) + 10( x - 18) = 25(x - 18)

8x + 192 + 10x - 180  = 25 x - 450   simplify

18x + 12  = 25x - 450

462 = 7x    divide by 7 on each side

x = 66  this is the number of 50 cent coins in the beginning

And x + 24 = (66 + 24) = 90 were 10 cent coins in the beginning

And notice that (3/4)y = (2/5) (x + 24)...  so y = (8/15)(66 + 24) = (8/15)(90) = 48 coins 

So....there were 48 20 cent coins originally

 

Now.....let's check the math....

The total number of coins after the spree =

[(4/5)(66 + 24) + (66 - 18) ]  = 120

And (66 - 18) = 48 of these were 50 cent coins

So..... 48 / 120 = 40% were 50 cent coins

And after the spree....there were an equal number of 10 and 20 cent coins.....check ...(2/5)(90) = (3/4)(48) = 36 each

 

So the total spent  = (3/5)(90)(.10) + (1/4)(48)(.20) + (18)(.50)  = $16.80 

 

  

 

I believe Melody has a slight error

She gets 210 10 cent  coins at the start    .....and 2/5 of these are left = 84 left   

And this is equal  to the number of 20 cent coins left

And she calculates the number of 50 cent coins left = 210 - 42 =  168

So....the total coins left = [ 84 + 84 + 168]  = 336 coins left

But 168 / 336 = 50% of the coins left are 50 cent coins......and this is too much

 

Can anyone reconcile these differences ???

CPhill  May 2, 2015
 #4
avatar+26328 
+10

Here's my check:

 Tanya's coins

This supports Chris's results.

.

Alan  May 2, 2015
 #5
avatar+78618 
+10

Thanks, Alan.....!!!

 

  

CPhill  May 2, 2015
 #6
avatar+78618 
+10
Best Answer

Addendum......I believe I spotted Melody's error

She has

0.72X  -  16.8 =X  - 42

16.8 + 42  =  x - 0.72X

 

But the 16.8 should be negative

So....it should be....

-16.8 + 42  = 0.28X

25.2  = 0.28X

X = 90  = the number of 10 cent coins, originally.....

And our answers would now agree....

Hey.....no biggie......!!!!

 

  

CPhill  May 2, 2015
 #7
avatar+91001 
+5

WOW Everyone's answers got white.  You didn't need to do that - I am a big girl   LOL

I have unwhited the whole thread  :)

Thanks Alan and Chris  :)    Three heads are always better than one    (especially when the one is mine lol)  

Melody  May 3, 2015

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