Q&A - PSLE Math

[sall]

tianzhu:

Michaelia0816:

Also this one, help!


The ratio of the average speed of Ali, Ben and Carl was 2:3:4 respectively. They started driving at the same time and after 5h, they had covered a total of 675 km. What was the average speed of Ben?

Hi

A:B:C --------2:3:4(Speed)
A:B:C --------2:3:4(Distance)
A:B:C --------4:3:2(Time)

Distance varies in direct proportion to speed.
Time is inverse proportion to speed.

9 units -------- 675
1 unit ------- 75
Ben -------- 3*75 ------- 225 km

For time, 9 units ------- 300 minutes
3 units ------- 100 mins or 5/3h

Average speed of Ben ------- 225/5/3 --------- 135 km/h

Best wishes

Hi Tianzhu, I noticed you did not use the '5 hr' in the working and if the average speed of Ben is 135km/h, then after 5 hr, the distance travelled by Ben is 675km. But 675km is the distance covered by the 3 men.

[tianzhu]

sall:

Hi Tianzhu, I noticed you did not use the '5 hr' in the working and if the average speed of Ben is 135km/h, then after 5 hr, the distance travelled by Ben is 675km. But 675km is the distance covered by the 3 men.

Hi

Thank you.

I've taken 5h as the total time for the 3 men.I'll do the revision.

Best wishes

[Michaelia0816]

Oh thank you so much , yet still got 5 question left even at 9 pm…

[Michaelia0816]

tianzhu:

sall:

Hi Tianzhu, I noticed you did not use the '5 hr' in the working and if the average speed of Ben is 135km/h, then after 5 hr, the distance travelled by Ben is 675km. But 675km is the distance covered by the 3 men.

Hi

We use 5h.

It's is converted into 300 minutes.

Best wishes

Yup, even I, the school pupils even uses h not hr as the question uses h not hr!

[tianzhu]

Michaelia0816:

tianzhu:

[quote=\"sall\"]Hi Tianzhu, I noticed you did not use the '5 hr' in the working and if the average speed of Ben is 135km/h, then after 5 hr, the distance travelled by Ben is 675km. But 675km is the distance covered by the 3 men.

Hi

We use 5h.

It's is converted into 300 minutes.

Best wishes

Yup, even I, the school pupils even uses h not hr as the question uses h not hr![/quote]Hi

Please see revised solution.

Best wishes.

[tianzhu]

superksmum:

Hi Tianzhu,


I have checked the paper. This is what is stated in the paper.

Hi

Speedmaths has given us some pointers.

The mass of water varies in direct proportion to its volume.

The ratio of the volume of water in the tank when it was 1/2 full to the volume of the water went he tank was 2/3 full -------- 3:4 ------- 6:8

The ratio of the mass of the tank when it was 1/2 full to the mass of the tank when it was 2/3 full was 7:9.

1 unit ------ 500g

The total mass of the tank and water when the tank was 2/3 full -------- 9*500 ------ 4500 g

Best wishes.

[Michaelia0816]

Help again with the following 3 questions!!!


The diagram shows the road linking town p to town q.
P to q distance is 280km!
Roy passed P at 10am and reached q at 2 pm. Sam drove from p to q at a constant speed of 100km/h and arrived at a at 1.48pm.
a) when did Roy leave p?
b) when Sam reached town q, how far away from town q was Roy?

[superksmum]

Hi supermum,


Try dividing the tank into 12 units:

1/2 filled ----- 6 units
2/3 filled ----- 8 units.

This should work for (b).

Can you work from here?

Cheers


speedmaths.com

PS

We have a Maths Workshop to teach parents how to solve similar questions.
You may wish to look up the "PSLE Maths Workshop for Parents" thread under the Happenings forum.


.[/quote]


Hi speedmaths,

Sorry, we are confused now. Is it possible to elaborate?

Thank you.

[superksmum]

Hi Speedmaths,

Sorry, just got to see the working from Tianzhu after posting.

Hi Tianzhu,
Will ask DD to try out and see whether she understand.

Thank you so much for your help.

[tianzhu]

Michaelia0816:

Help again with the following 3 questions!!!!!!


The diagram shows the road linking town p to town q.
P to q distance is 280km!
Roy passed P at 10am and reached q at 2 pm. Sam drove from p to q at a constant speed of 100km/h and arrived at a at 1.48pm.
a) when did Roy leave p?
b) when Sam reached town q, how far away from town q was Roy?

Hi

Roy or Sam?

Best wishes