Q&A - PSLE Math

[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

[MathIzzzFun]

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?

8am to 11.30am --> 3.5h
At any time, 8 will play. So,
total available play time --> 8 x 3.5h = 28 h

play time per person --> 28 h/10 = 2.8h = 168 min

cheers.

[MathIzzzFun]

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?

thanks

Total number of white balls : black balls --> 6 units : 1 unit + 20

If 50 white balls are removed:

Number of white balls : black balls --> 4 x ( 1 units + 20) : 1 unit + 20

total white balls:
6 units = 4 units + 80 + 50
1 unit --> 65

Total number of balls --> 7 x 65 + 20 = 475

cheers.

[MathIzzzFun]

ozora:

Need some pointers on the following questions using units methods



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

similar questions here :

- http://www.flickr.com/photos/62167097@N02/7080366811/in/set-72157629537287046

- http://www.flickr.com/photos/62167097@N02/6858744276/in/set-72157629537287046

Total, black balls → 750
Total, white balls → 600
Total, black and white balls → 1350

In the end:
Total, black balls : ½ Box A + ¾ Box B →750
Total, white balls: ½ Box A + ¼ Box B → 600
½ Box B → 750 – 600 = 150
Box B → 300
Box A → 1350 – 300 = 1050

Balls moved from Box B to Box A :
Black balls → 400 – ¾ x 300 = 175
White balls → 100 – ¼ x 300 = 25


cheers.

[ozora]

MathIzzzFun:

ozora:

Need some pointers on the following questions using units methods



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

similar questions here :

- http://www.flickr.com/photos/62167097@N02/7080366811/in/set-72157629537287046

- http://www.flickr.com/photos/62167097@N02/6858744276/in/set-72157629537287046

Total, black balls → 750
Total, white balls → 600
Total, black and white balls → 1350

In the end:
Total, black balls : ½ Box A + ¾ Box B →750
Total, white balls: ½ Box A + ¼ Box B → 600
½ Box B → 750 – 600 = 150
Box B → 300
Box A → 1350 – 300 = 1050

Balls moved from Box B to Box A :
Black balls → 400 – ¾ x 300 = 175
White balls → 100 – ¼ x 300 = 25


cheers.

this is definite clearer to understand. I got stuck trying to use the methods provided by the previous examples.

after trf:
Black : white
Box A -> 1triangle: 1 triangle

Box B-> 3 diamonds: 1 diamond.

I do not know how to equate and divide by how many. so how do i go about doing that

as for Q1: i got it and redraw it as below.
http://i50.tinypic.com/tagcg7.jpg\">

[MathIzzzFun]

ozora:

MathIzzzFun:

Need some pointers on the following questions using units methods



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.

similar questions here :

- http://www.flickr.com/photos/62167097@N02/7080366811/in/set-72157629537287046

- http://www.flickr.com/photos/62167097@N02/6858744276/in/set-72157629537287046

Total, black balls → 750
Total, white balls → 600
Total, black and white balls → 1350

In the end:
Total, black balls : ½ Box A + ¾ Box B →750
Total, white balls: ½ Box A + ¼ Box B → 600
½ Box B → 750 – 600 = 150
Box B → 300
Box A → 1350 – 300 = 1050

Balls moved from Box B to Box A :
Black balls → 400 – ¾ x 300 = 175
White balls → 100 – ¼ x 300 = 25


cheers.

this is definite clearer to understand. I got stuck trying to use the methods provided by the previous examples.

after trf:
Black : white
Box A -> 1triangle: 1 triangle

Box B-> 3 diamonds: 1 diamond.

I do not know how to equate and divide by how many. so how do i go about doing that

as for Q1: i got it and redraw it as below.
http://i50.tinypic.com/tagcg7.jpg\">

Using units and parts :

Total, black balls → 750
Total, white balls → 600
Total, black and white balls → 1350

IN the end,
Black balls : White Balls, in Box A --> 1u : 1u (1 triangle : 1 triangle)
Black balls : White Balls, in Box B --> 3p : 1p (3 diamonds : 1 diamond)

Total black balls: 1u + 3p = 750
Total white balls: 1u +1p = 600
So, 2p --> 750 - 600 = 150
1p --> 75
1u --> 600 - 75 = 525

Number of balls moved from B to A:
Black --> 400 - 3 x 75 = 175
White --> 100 - 75 = 25

cheers.