Q&A - PSLE Math

[ozora]

MathIzzzFun:

ozora:

need help in this question.

Sam has a bag of 20 cents coins and a bag of 50 cents coins. The number of 20 cents coins is double the number of 50 cents coins.
Sam takes out three 50 cents coins and four 20 cents coins each time.
After a few rounds, he found that there are eighteen 20 cents coins and 1 50 cents coin left. How much money did Sam have?
thanks

Total number coins - number of coins left = number coins removed

At first,
number of 20c coins : 50c coins --> 2u : 1u

Coins removed,
number of 20c coins : 50c coins
--> 2u - 18 : 1u -1
= 4 : 3

cross multiply/equalize:

6u - 54 = 4u - 4
1u --> 25

total amount of money --> 4 x 25 x $0.20 + 1 x 25 x $ 0.50 = $ 32.50

cheers.

thanks MathsIzzFun. got it. is there an error in : 4 x 25 x $0.20 ? should it be 2 x25 x0.2?
do we ignore the After a few rounds, he found that there are eighteen 20 cents coins and 1 50 cents coin left

[MathIzzzFun]

ozora:

MathIzzzFun:

[quote=\"ozora\"]need help in this question.

Sam has a bag of 20 cents coins and a bag of 50 cents coins. The number of 20 cents coins is double the number of 50 cents coins.
Sam takes out three 50 cents coins and four 20 cents coins each time.
After a few rounds, he found that there are eighteen 20 cents coins and 1 50 cents coin left. How much money did Sam have?
thanks

Total number coins - number of coins left = number coins removed

At first,
number of 20c coins : 50c coins --> 2u : 1u

Coins removed,
number of 20c coins : 50c coins
--> 2u - 18 : 1u -1
= 4 : 3

cross multiply/equalize:

6u - 54 = 4u - 4
1u --> 25

total amount of money --> 4 x 25 x $0.20 + 1 x 25 x $ 0.50 = $ 32.50

cheers.

thanks MathsIzzFun. got it. is there an error in : 4 x 25 x $0.20 ? should it be 2 x25 x0.2?
do we ignore the After a few rounds, he found that there are eighteen 20 cents coins and 1 50 cents coin left[/quote]Thanks for pointing out the error.
The 'After a few rounds, he found that there are eighteen 20 cents coins and 1 50 cents coin left' is needed because this gives us the leftover coins after removing in the ratio of 4:3.

using units/parts, we get
at first, 20c:50c -> 2u : 1u
Coins removed, 20c:50c -> 4p : 3p
18 20c and 1 50c left, so
2u - 4p = 18
1u - 3p = 1
and then solving for u/p

cheers

[starfish53]

Can anyone help me with the following question?



1) A blouse cost 4/5 as much as a dress. Serena spent 3/8 of her money on 3 blouses. She also bought 2 dresses. What fraction of her money did she spend altogether?


2) Ivan divided 64 guppies into 4 bowls A to D. 7 guppies were transferred from Bowl A to Bowl B, 3 guppies were moved from Bowl C to Bowl B and 9 guppies were moved from Bowl C to Bowl D. All the bowls then had an equal number of guppies. Express in ratio the sum of the number of guppies in Bowl A and B at first to the sum of the number of guppies in Bowl C and D at first.


Thanks in advance.

[Maths Hub]

starfish53:

Can anyone help me with the following question?



1) A blouse cost 4/5 as much as a dress. Serena spent 3/8 of her money on 3 blouses. She also bought 2 dresses. What fraction of her money did she spend altogether?


2) Ivan divided 64 guppies into 4 bowls A to D. 7 guppies were transferred from Bowl A to Bowl B, 3 guppies were moved from Bowl C to Bowl B and 9 guppies were moved from Bowl C to Bowl D. All the bowls then had an equal number of guppies. Express in ratio the sum of the number of guppies in Bowl A and B at first to the sum of the number of guppies in Bowl C and D at first.


Thanks in advance.

1) 3 blouses-->3/8
1 blouse--> 1/8
1 dress-->5/4 X 1/8= 5/32
2 dresses--> 5/16
3 blouses + 2 dresses--> 3/8+5/16 = 11/16

2) This is a working backwards question. The most important information is \"All the bowls then had an equal number of guppies. \"

End
A:B:C:D
16:16:16:16

Before \"9 guppies were moved from Bowl C to Bowl D\"
A:B:C:D
16:16:25:7

Before \"3 guppies were moved from Bowl C to Bowl B\"
A:B:C:D
16:13:28:7

Before \"7 guppies were transferred from Bowl A to Bowl B\"
A:B:C:D
23:6:28:7

Therefore:
A+B:C+D
29:35

Hope that helps.

[SZ Venture]

starfish53:

Can anyone help me with the following question?



1) A blouse cost 4/5 as much as a dress. Serena spent 3/8 of her money on 3 blouses. She also bought 2 dresses. What fraction of her money did she spend altogether?


2) Ivan divided 64 guppies into 4 bowls A to D. 7 guppies were transferred from Bowl A to Bowl B, 3 guppies were moved from Bowl C to Bowl B and 9 guppies were moved from Bowl C to Bowl D. All the bowls then had an equal number of guppies. Express in ratio the sum of the number of guppies in Bowl A and B at first to the sum of the number of guppies in Bowl C and D at first.


Thanks in advance.

1) 1 blouse would cost her 1/8 of her money. 1 dress would cost her 5/4 of 1/8 = 5/32 of her money. (you can try to draw modal)

2 dresses would be 10/32 of her money.
3 blouses would be 3/8 of her money.

10/32 + 3/8 = 22/32 = 11/16.

Qn2) using the method of starting from the back + modal drawing.

4 bowls have a total of 64 guppies. at the end, each bowl has the same number, which means 64/4 = 16 guppies each.

\"9 guppies were moved from Bowl C to Bowl D\"
means that D has only 16-9 = 7 guppies at first.
C would have 16 + 9 = 25 before moving from C to D.

\"3 guppies were moved from Bowl C to Bowl B\"
means that B has 16-3 = 13 guppies
C would have 25+3 =28 before moving from C to B.

\" 7 guppies were transferred from Bowl A to Bowl B\"
means that A has 16+7 = 23 guppies at first
B has 13-7= 6 guppies.

therefore,
A+B at first = 23 + 6 = 29
C+D at first = 28 + 7 = 35

ratio : 29 : 35

[sokk]

I need help for this question.


Rita and Molly shared some stickers between them.
If Rita gives 15 of her stickers to Molly, Molly will have thrice as many stickers as Molly.
If Molly gives 15 of her stickers to Rita, Rita will have twice as many stickers as Molly.
How many stickers does each of them have?



Thanks!!

[Maths Hub]

sokk:

I need help for this question.


Rita and Molly shared some stickers between them.
If Rita gives 15 of her stickers to Molly, Molly will have thrice as many stickers as Molly.
If Molly gives 15 of her stickers to Rita, Rita will have twice as many stickers as Molly.
How many stickers does each of them have?


Thanks!!

Hi, I presume you mean

Rita and Molly shared some stickers between them.
If Rita gives 15 of her stickers to Molly, Molly will have thrice as many stickers as Rita.
If Molly gives 15 of her stickers to Rita, Rita will have twice as many stickers as Molly.
How many stickers does each of them have?

1) If Rita gives 15 of her stickers to Molly, Molly will have thrice as many stickers as Rita.

Molly: 3 units
Rita: 1 unit

2) Start (If Rita didn't gives 15 of her stickers to Molly)

Molly: 3 units -15
Rita: 1 unit + 15

3) If Molly gives 15 of her stickers to Rita

Molly: 3 units - 30
Rita: 1 unit + 30

Now, Rita has twice of Molly, meaning
(3 units - 30) X 2 --> 1 unit + 30
6 units - 60 --> 1 unit + 30
5 units --> 90
1 unit--> 18

Therefore Molly at start: 3 units - 15 --> 3 X 18 - 15 = 54 - 15 = 39
Rita at start: 1 unit + 15 --> 18 + 15 = 33

Hope that helps.

[sokk]

Maths Hub:

sokk:

I need help for this question.


Rita and Molly shared some stickers between them.
If Rita gives 15 of her stickers to Molly, Molly will have thrice as many stickers as Molly.
If Molly gives 15 of her stickers to Rita, Rita will have twice as many stickers as Molly.
How many stickers does each of them have?


Thanks!!

Hi, I presume you mean

Rita and Molly shared some stickers between them.
If Rita gives 15 of her stickers to Molly, Molly will have thrice as many stickers as Rita.
If Molly gives 15 of her stickers to Rita, Rita will have twice as many stickers as Molly.
How many stickers does each of them have?

1) If Rita gives 15 of her stickers to Molly, Molly will have thrice as many stickers as Rita.

Molly: 3 units
Rita: 1 unit

2) Start (If Rita didn't gives 15 of her stickers to Molly)

Molly: 3 units -15
Rita: 1 unit + 15

3) If Molly gives 15 of her stickers to Rita

Molly: 3 units - 30
Rita: 1 unit + 30

Now, Rita has twice of Molly, meaning
(3 units - 30) X 2 --> 1 unit + 30
6 units - 60 --> 1 unit + 30
5 units --> 90
1 unit--> 18

Therefore Molly at start: 3 units - 15 --> 3 X 18 - 15 = 54 - 15 = 39
Rita at start: 1 unit + 15 --> 18 + 15 = 33

Hope that helps.

Hi,
Thanks for the quick reply. But when I try to work out the story using Rita 33 and Molly 39 at first, I can't seems to get Rita having twice as many as Molly .

At first
Rita 33 Molly 39

after Rita gives Molly 15
Rita 18 , Molly 54
(Molly has thrice as many as Rita)

after Molly gives Rita 15
Rita 33 , Molly 39
(I can't arrive at Molly having twice..)

Did I interpret the question wrongly??
Please help! getting confuse....

[Maths Hub]

sokk:

Hi,
Thanks for the quick reply. But when I try to work out the story using Rita 33 and Molly 39 at first, I can't seems to get Rita having twice as many as Molly .

At first
Rita 33 Molly 39

after Rita gives Molly 15
Rita 18 , Molly 54
(Molly has thrice as many as Rita)

after Molly gives Rita 15
Rita 33 , Molly 39
(I can't arrive at Molly having twice..)

Did I interpret the question wrongly??
Please help! getting confuse....

Hi,

After Molly give Rita 15
Rita 48, Molly 24
(Rita is twice Molly, not the other way round)

Hope that helps.

[sokk]

.