Q&A - PSLE Math

[pixiedust]

tianzhu, thank you very much for the tips regarding speed questions. much appreciated !


Appreciate help with this question :
http://i1197.photobucket.com/albums/aa424/pixie_dust8/circle1.jpg\">

[2DMommy]

tianzhu:

2DMommy:

Please help me with these two questions :


1) Sally has a bottle containing some red and blue beads. If she adds another 10 red beads, 60% of the beads in the bottle are blue. If she adds another 30 blue beads, 75% of the beads in the bottle are blue. How many red beads are in the bottle ?
Thank you !

Hi

Where is your Q1 from?

Sometimes, the introduction of the word “another” in the conditions can be opened to interpretation.

This question has been floating around regularly in forums.

I have some red and blue ribbons in a bottle.
If I add 20 red ribbons, 60% of my ribbons are blue.
If I add another 60 blue ribbons, 75% of my ribbons are blue.
How many ribbons do I have in the bottle?

Depending on one’s interpretation of the word another in the second condition, one may end up with 180 or 80.

It’ll be helpful if current PSLE students or their parents help to clarify with their school teachers on this question.

For your Q1, I’m more inclined to go for

First scenario
Red beads ------ 2 units – 10
Blue beads ------ 3 units

Second scenario
Red beads ------ 2 units - 10 -------- 1 part
Blue beads ------ 3 units + 30 ------- 3 parts

6 units – 30 -------- 3 units + 30

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

Number of red beads -------- 30

Best wishes

Hi Tianzhu, this question was actually taken from my ds enrichment's homework. We are actually quite confuse too, I will get him to clarify with this teacher and will try to post the method when his teacher goes through with them next week. Thank you

[Winx5015]

Hi,


Got a question on Average,Rate and Speed.

(1). Town P and Town Q are 770km apart. At 6am, a car left Town P for Town Q at an average speed of 70km/h. 6 hours later, a truck set off from Town Q for Town P at an average speed of 80km/h. At what time would the two vehicles pass each other?

Thanks:)

[tianzhu]

pixiedust:

tianzhu, thank you very much for the tips regarding speed questions. much appreciated !


Appreciate help with this question :
http://i1197.photobucket.com/albums/aa424/pixie_dust8/circle1.jpg\">

Hi

You’re welcome.

Imagine the longest length (12cm) of the triangle as the diagonal of a rectangle.

You’ll be able to find the breadth of the rectangle which is also the base of the triangle.

Area of rectangle ----- 2*35 ------- 70
Height ------ 10 (radius of quadrant)
Breadth ------ 70/10 ------ 7

From here, I’ll leave it to you to do the rest of the solution.

Best wishes

[Andrew Lee]

Q7. Cindy planeed to cycle from Town G to Town H.If she were to cycle at 9km/h, she would reach Town H at 8.45pm. If she were to cycle at 12KM/h, she would reach Town H at 8.15pm.What was the distance between Town G & Town H?


Q16…
A tank with a square bas is 40% filled with water. When 60% of the water is poured out, the height of the water falls by 9.6cm. 120.96 lite of water is poured in to fill the tank to the brim. What is the ratio of the height of the tank to one side of its base ? (simple form)

[Andrew Lee]

http://i44.tinypic.com/2akek2x.jpg\">

[tianzhu]

Winx5015:

Hi,


Got a question on Average,Rate and Speed.

(1). Town P and Town Q are 770km apart. At 6am, a car left Town P for Town Q at an average speed of 70km/h. 6 hours later, a truck set off from Town Q for Town P at an average speed of 80km/h. At what time would the two vehicles pass each other?

Thanks:)

Hi

As in any questions on Speed, it’s useful to have some form of pictorial representation.

6h from 6am ------- 12 noon

At 12 noon, the car ------- 6*70 or 420 km from Town P (say at point R)

At 12 noon, a truck moved from Town Q and the car continued to move towards Town Q from point R.

From R to Q, the distance ------- 770 - 420 ------ 350

In 1h, the car and truck travelled 150km together.

350/150 ------ 2 1/3 (2h 20min)

Time when they pass each other ------ 2.20 pm.

Best wishes

[tianzhu]

Andrew Lee:

Q7. Cindy planeed to cycle from Town G to Town H.If she were to cycle at 9km/h, she would reach Town H at 8.45pm. If she were to cycle at 12KM/h, she would reach Town H at 8.15pm.What was the distance between Town G & Town H?


Q16..
A tank with a square bas is 40% filled with water. When 60% of the water is poured out, the height of the water falls by 9.6cm. 120.96 lite of water is poured in to fill the tank to the brim. What is the ratio of the height of the tank to one side of its base ? (simple form)

Hi

Q1)

Speed ratio ------ 3:4 (9:12)
Time ratio ------ 4:3

1 unit ------ ½ h
3 units ------ 1.5h

Distance between G and H ------ 1.5*12 -------18 km

Q2)

40%*60% -------24%
Amount of water left ------- 16%

Volume
84% -------- 120960 cubic cm
100% ------- 144000 cubic cm

Height
24% ------- 9.6cm
100% ------- 40 cm

Area of square base ------ 144000/40 ------- 3600
One side of square base ------- 60

40:60 ------2:3

Best wishes

[tianzhu]

Andrew Lee:

http://i44.tinypic.com/2akek2x.jpg\">

Hi

A:B ------ 4:5 ------- 16:20
B:C ------4:5 --------20:25

Shaded area of A ------- 12 units
Unshaded area of A ------- 4 units

Unshaded area of C ------- 25 - 12 ------13 units

Unshaded area of A/ Unshaded area of C ------- 4/13

Percentage of figure shaded ------- 12/(25+4) -------12/29 ------ 41%

Best wishes

[Winx5015]

Hi tianzhu,


Thanks for your help.

Have a wonderful weekends