Q&A - PSLE Math

[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.

[MathIzzzFun]

ozora:

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

The units approach was used in the posted solution as this method could be understood by P4 students. The solution can be directly translated into a MD solution replacing the units with model blocks.

Here's a solution using the units-parts or UP approach:

http://i48.tinypic.com/3148efb.png\">

cheers.

[ozora]

MathIzzzFun:

ozora:

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

The units approach was used in the posted solution as this method could be understood by P4 students. The solution can be directly translated into a MD solution replacing the units with model blocks.

Here's a solution using the units-parts or UP approach:

http://i48.tinypic.com/3148efb.png\">

cheers.

great thanks to u.

[ozora]

Need some guide again in the following question.

John had some money. He spent it all in 3 stores. In each store, he spent $2 more than half of what he had when he entered.
a(how much did he spend at the last store?
b)how much did he have at first

[MathIzzzFun]

ozora:

Need some guide again in the following question.

John had some money. He spent it all in 3 stores. In each store, he spent $2 more than half of what he had when he entered.
a(how much did he spend at the last store?
b)how much did he have at first

Total amount at first ---> 8 units
At 1st store, spent --> 4 units + $2, Left --> 4 units - $2
At 2nd store, spent --> 2 units - $1 + $2 = 2 units + $1, Left --> 2units - $3
At 3rd store, spent --> 1 unit -$1.5 + $2 = 1 unit + $0.5

At 3rd store, he spent all that he had left, so

2 units - $3 = 1unit + $0.5
1 unit --> $3.5

at 3rd store, he spent --> $4
total amount he had --> $28

cheers.

[Oracle]

Hi, could any of you Math Guru help me with this p6 math question please:


It takes Eleanor 8 hours to make a quilt by herself. If Kelly helps her, they will take 3 hours to make the quilt. How long would Kelly have taken if she makes the quilt by herself? Express your answer in hours and minutes.

Thanks a lot!

[MathIzzzFun]

Oracle:

Hi, could any of you Math Guru help me with this p6 math question please:


It takes Eleanor 8 hours to make a quilt by herself. If Kelly helps her, they will take 3 hours to make the quilt. How long would Kelly have taken if she makes the quilt by herself? Express your answer in hours and minutes.

Thanks a lot!

Total amount of work to make the quilt --> 24 units (LCM of 3 &
Eleanir work rate --> 24 units/8h = 3 units /h
Eleanor & Kelly work rate --> 24 units /3h = 8 units/h
Kelly work rate --> 5 units/h
time taken by Kellt alone -> 24/5 h = 4. 8h = 4h 48min

cheers.

[Oracle]

Thank you.

[Bunny27]

Oracle:

Thank you.

Pls help on this question:

1. Melissa had 325 beads. 60% of them were red while the rest were green. After using some red beads, the percentage of red beads decreased to 35%.
How many red beads did she use?

Thanks

[MathIzzzFun]

Bunny27:

Oracle:

Thank you.

Pls help on this question:

1. Melissa had 325 beads. 60% of them were red while the rest were green. After using some red beads, the percentage of red beads decreased to 35%.
How many red beads did she use?

Thanks

At first,
red beads --> 60% x 325 = 195
green beads --> 325 - 195 = 130

in the end,
green beads --> 130 (no change) --- 65%
1% --> 2

red beads --> 35% --> 70
red beads, used --> 195 - 70= 125

cheers