Q&A - PSLE Math

[smileplease]

Need help on this Q:


Ginny had two boxes of greeting cards. After she had transferred 1/5 of the greeting cards in box A to box B, the ratio of the number of greeting cards in box A to the number of greeting cards in box B is 3:5. What was the ratio of the number of greeting cards in box A to the number of greeting cards in box B at first?

[MathIzzzFun]

smileplease:

Need help on this Q:


Ginny had two boxes of greeting cards. After she had transferred 1/5 of the greeting cards in box A to box B, the ratio of the number of greeting cards in box A to the number of greeting cards in box B is 3:5. What was the ratio of the number of greeting cards in box A to the number of greeting cards in box B at first?

Hi

after transfer, Box A : Box B = 3 : 5 = 12u : 20u
Before transfer, Box A = 5/4 x 12u = 15u

Before transfer, Box A : Box B = 15u : 20u-3u = 15: 17

cheers.

[MathIzzzFun]

Angel25:

Pls HELP!!



Roy jogged from his house to the playground and back at 10km/h. He reached home at 12.18pm. If he jogged at 3km/h slower, he would reach home at 1.30pm. If he wanted to reach home at 12.45pm to have his lunch, at what speed did he have to jog?

Thanks!!

Hi

speed ratio, initial : slower = 10 : 7
time ratio, initial : slower = 7: 10

1330-1218 = 72min = 1 1/5h
so 3u = 1.2h, 7u = 1.2/3 x7 = 2.8h = 2h 48min

To reach home at 12.45pm, means to take 1245-1218 = 27min more, ie total time to jog at new speed = 2h 48 min + 27min = 3h 15 min = 3.25h

new speed = 2.8/3.25 x 10 km/h= 112/13 km/h = 8 8/13 km/h

cheers.

[pensiveowl]

Pls help with this question thanks:


Mr Ho and Mrs Lee took part in a chess competition. Mr Ho played against 1/3 as many men as women. Mrs Lee played against 2/5 as many men as women. How many women took part in the chess competition?

[pensiveowl]

Could someone pls help with this one as well - thanks


The ratio of the number of green marbles to the red marbles in a box is 6 : 5. After 60 green marbles and 60 red marbles were removed from the box. the ratio of the number of green marbles to red marbles became 9 : 7. How many red marbles were there in the box at first?

[tianzhu]

Hi


CHS P6 Prelim Q16 2010

I’ve attempted to breakdown the question into familiar shapes which students are familiar with.

PLSE students should be very comfortable with familiar shapes such as triangle, circles, and squares. They should also be able to find out the area of the eye or leaf or rugby ball.

I’ll leave it to you to work out the detailed calculations as students may have their preferred way of working out the circumferences and areas of shapes. For example some students may prefer to calculate the area of the triangle while others may want to find out the areas of two small squares (10).

Hope this helps.

Best wishes.

http://farm7.static.flickr.com/6166/6170513303_5b7ea9a81d_z.jpg\">

[tianzhu]

pensiveowl:

Could someone pls help with this one as well - thanks


The ratio of the number of green marbles to the red marbles in a box is 6 : 5. After 60 green marbles and 60 red marbles were removed from the box. the ratio of the number of green marbles to red marbles became 9 : 7. How many red marbles were there in the box at first?

Hi

The number of green marbles and red marbles removed from the box are the same.

Hence the difference between the number of green marbles and red marbles stay the same before and after.

At first.
Green: Red ------ 6:5 -------12:10
Difference ----- 1 ------ 2

In the end
Green: Red ------ 9:7
Difference ----- 2

Make the difference the same.

3 units ------ 60
1 unit ------ 20

At first, red marbles -------10*20 -------200

Best wishes

[MathIzzzFun]

pensiveowl:

Could someone pls help with this one as well - thanks


The ratio of the number of green marbles to the red marbles in a box is 6 : 5. After 60 green marbles and 60 red marbles were removed from the box. the ratio of the number of green marbles to red marbles became 9 : 7. How many red marbles were there in the box at first?

Hi

the two questions are similar, but for q2, the concept of \"same gap\" can be applied to solve.

q1. Mr Ho and Mrs Lee took part in a chess competition. Mr Ho played against 1/3 as many men as women. Mrs Lee played against 2/5 as many men as women. How many women took part in the chess competition?

Mr Ho played 1/3 as many men as women --> men : women = 1u : 3u
..total number of men = 1u + 1

Mrs Ho played 2/5 as many men as women
--> men : women = 1u + 1 : 3u -1 = 2 : 5

cross-multiply: 5u+5 = 6u -2, 1u = 7

Number of men = 1u + 1 = 8
Number of women = 3u = 21

q2. The ratio of the number of green marbles to the red marbles in a box is 6 : 5. After 60 green marbles and 60 red marbles were removed from the box. the ratio of the number of green marbles to red marbles became 9 : 7. How many red marbles were there in the box at first?

at first, green : red = 6u : 5u
in the end, green : red = 6u - 60 : 5u - 60 = 9 : 7
so, 42u - 420 = 45u - 540, 3u = 120, 1u = 40

At first, red marbles = 5u = 200

using \"same gap/difference\":

in the end, green : red = 9u : 7u (gap 2u)
at first, green : red = 6 : 5 = 12u : 10 u (gap 2u)
so 3u = 60, 1u = 20

Number of red marbles at first = 10u = 200

cheers.

[pensiveowl]

tianzhu:

pensiveowl:

Could someone pls help with this one as well - thanks


The ratio of the number of green marbles to the red marbles in a box is 6 : 5. After 60 green marbles and 60 red marbles were removed from the box. the ratio of the number of green marbles to red marbles became 9 : 7. How many red marbles were there in the box at first?

Hi

The number of green marbles and red marbles removed from the box are the same.

Hence the difference between the number of green marbles and red marbles stay the same before and after.

At first.
Green: Red ------ 6:5 -------12:10
Difference ----- 1 ------ 2

In the end
Green: Red ------ 9:7
Difference ----- 2

Make the difference the same.

3 units ------ 60
1 unit ------ 20

At first, red marbles -------10*20 -------200

Best wishes

Thanks Tianzhu!

[TT2]

Hi, how to do this qn?


Given that p:(q+r)=1:3, r:(q+s)=1:2 and p:s=2:5.
(a) find p:q:r:s
(b) find (r+q):(p+s)

Thank you