Q&A - PSLE Math

[ftwm]

2/5 of my sister’s beads are yellow. 7/13 of the remaining beads are green. The rest of the beads are black. If there are 32 more yellow beads than black beads, how many beads are green?

[MathIzzzFun]

ftwm:

2/5 of my sister's beads are yellow. 7/13 of the remaining beads are green. The rest of the beads are black. If there are 32 more yellow beads than black beads, how many beads are green?

Remainder --> 3/5 of beads

Green --> 7/13 x 3/5 of beads = 21/65 of beads
Black --> 6/13 x 3/5 of beads = 18/65 of beads
Yellow --> 2/5 of beads = 26/65 of beads

26/65 - 18/65 = 8/65
8/65 of beads --> 32
21/65 of beads --> 84

There are 84 green beads

cheers.

[speedmaths.012624com]

ftwm:

2/5 of my sister's beads are yellow. 7/13 of the remaining beads are green. The rest of the beads are black. If there are 32 more yellow beads than black beads, how many beads are green?

Hi ftwm,

One possible method:

Look at the denominators; 5 and 13.
The denominators are your friends.

5 x 13 = 65

Let there be 65 boxes of beads

2/5 of my sister's beads are yellow
2/5 x 65 = 26
26 boxes contain yellow beads

Remaining = 65 - 26 = 39 boxes

7/13 of the remaining beads are green
7/13 x 39 = 21
21 boxes contain green beads

Remaining = 39 - 21 = 18 boxes
18 boxes contain black beads

26 boxes contain yellow beads
18 boxes contain black beads

There are 26 - 18 = 8 more boxes of yellow than black beads
there are 32 more yellow beads than black beads

8 boxes contain 32 beads

1 box contains ??? beads

Can you work from here?

Cheers


speedmaths.com

[mathnoobs]

MathIzzzFun:

mathnoobs:

I was going through some old posts and saw this problem which I'm very confused on what it means:


Siti had some money. She gave some money to Kelly and Lindy and saved the rest. The ratio of her savings to the amount she gave away was 5: 8. The ratio of Kelly's money to Lindy's money was 5: 3 at first. After Kelly's money increased by $128 and Lindy's money decreased by $128, the ratio of Kelly's money to Lindy's money became 3: 1. How much money did Siti save?

Mathizzfun, you've provided a solution in http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=68&t=25129&start=1240
However, I don't quite understand the solution.
Siti's savings : Kelly's money : Lindy's money
--> 5u: 5u : 3u

I understood that:
Siti's original sum of money(Before) - money given to Kelly and Lindy = Siti's savings (After)
Thus Siti's Savings (After) = 5u
Money given to Kelly and Lindy = 8u
Siti's original sum of money (Before) = 13u
Based on this, I don't quite understand how you equate 5u:5u:3u.
There seems to be no relationship between Siti's 5u (After) and Kelly:Lindy ratio (5:3) (Before)

I also have a query on this part:
Kelly's money : Lindy's money --> 5u + $128 : 3u - $128 = 3 : 1
From the question, it seems that Kelly's money (After) = 5u + 128 + amt given by Siti
and Lindy's money (After) = 3u - 128 + amt given by Siti
what happened to the amount given by Siti ? :?

My interpretation of the question is:

http://i49.tinypic.com/15hledl.png\">

cheers.

Thank you very much MathIzzFun. I see how you've interpreted the problem. It is an uncommon way to structure the problem in this way.

[ftwm]

Thanks MathIzzzFun & Speedmaths.com. I’ve got it.

[ozora]

MathIzzzFun:

ozora:

need some help in these question.

Jean had some stamps. She gave Kay 1/3 of her stamps plus 6 more. she gave Liz 1/3 of her remaining stamps plus 4 more. If Jean finally had half as many stamps as Liz, how many stamps did Kay receive? my answer is 15.
Besides model drawing, how to use unitary method to solve?
is it similiar to http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=69&t=280&start=8620?

\"Kay\" was missing in the question - I have inserted as shown in blue above.

Jean --> 9 units
Kay --> 3 units + 6
Remainder --> 6 units - 6

Liz --> 2 units - 2 + 4 = 2 units + 2
Jean --> 4 units -4 - 4 = 4 units - 8
Jean had half as many as Liz
8 units - 16 = 2 units + 2
6 units --> 18, 1 unit --> 3

Kay --> 15
cheers.

thanks Maths. So I assumed Jean has 9 units as is a multiple of 3. ease of calculation?

[MathIzzzFun]

ozora:

MathIzzzFun:

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

Jean had some stamps. She gave Kay 1/3 of her stamps plus 6 more. she gave Liz 1/3 of her remaining stamps plus 4 more. If Jean finally had half as many stamps as Liz, how many stamps did Kay receive? my answer is 15.
Besides model drawing, how to use unitary method to solve?
is it similiar to http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=69&t=280&start=8620?

\"Kay\" was missing in the question - I have inserted as shown in blue above.

Jean --> 9 units
Kay --> 3 units + 6
Remainder --> 6 units - 6

Liz --> 2 units - 2 + 4 = 2 units + 2
Jean --> 4 units -4 - 4 = 4 units - 8
Jean had half as many as Liz
8 units - 16 = 2 units + 2
6 units --> 18, 1 unit --> 3

Kay --> 15
cheers.

thanks Maths. So I assumed Jean has 9 units as is a multiple of 3. ease of calculation?[/quote]yes (1/3 x 2/3 = 2/9 --> denominator is 9) , so that we work with whole numbers.

cheers.

[ozora]

thanks Maths. So I assumed Jean has 9 units as is a multiple of 3. ease of calculation?[/quote]


yes (1/3 x 2/3 = 2/9 –> denominator is 9) , so that we work with whole numbers.

cheers.[/quote]
thanks

[ginginboy]

Hi,


I need help to solve the following question, hope someone can provide detail guide. Thanks in advance.

On a certain day, 10 friends booked 2 badminton courts from 8 am to 11.30am and took turns to play games on them. At any time, only 8 of them played on the 2 badminton courts while the other 2 friends watched. If each of them had the same amount of playtime, how many minutes did each person play on the court?

[ozora]

Need some pointers on the following questions using units methods

a) There were black and white balls in a bag.
If 20 black balls are removed from the bag, the total number of balls left will be 7 times the number of black balls left.
If 50 white balls are removed from from the bag, the total number of balls left will be 5 times the number of black balls left.
How many balls are there in the bag?


b) Box A contains 350 black balls and 500 white balls.
Box B contains 400 black balls and 100 white balls.
How many black and white balls must be removed from Box B to Box A in order to have 50% of marbles in A are black and 75% of the marbles in B are black.
thanks