Q&A - PSLE Math

[jjxy mum]

tianzhu:

jjxy mum:

Hi,

I need help on this question .

Cynthia walked to the library from school and at the same time, Mrs
Lee walked to school from the library. If they walked towards each other, they would meet 4 min later. If they walked in the same direction, it would take Cynthia 20 mins to catch up with Mrs Lee whose walking speed was 40 m/min. How far was the library from the school? Assume that Mrs Lee's walking speed was constant at all times. ( Ans: 400m)

Hi

This question has been discussed before.

As in any Speed questions, start with a simple diagram.

In 20 minutes, Mrs Lee covered 20*40 or 800 m

In 4 minutes, Mrs Lee covered 4*40 or 160 m

In 16 minutes, CYTHNIA covered 960 m (800+160)

In 4 minutes, CYTHNIA covered 240 m (960/4)

Distance between library and school ------- 400 m (240+160)

Best wishes

Hi,

Thank you for your reply, we are still quite confused on the Cynthia's portion.

[tianzhu]

jjxy mum:

Hi,

Thank you for your reply, we are still quite confused on the Cynthia's portion.

Hi

Ok, managed to find the pictorial, hope this helps.

Best wishes

http://farm9.staticflickr.com/8155/7674972602_fac8ddb8c5_z.jpg\">

[shell]

Hi


A neat way is to use MD.

Due to time constraints, I’ll work using units.

2/3 of the total value of the twenty-cent coins is the same as 1/2 of the total value of the fifty-cent coins.

Total value of twenty-cent coins ------ 3 units

Total value of fifty-cent coins ------ 4 units

If Beatrice spends 4 fifty-cent coins, the value of the twenty-cent coins and the value of the remaining fifty-cent coins will be the same.

4 fifty-cent coins ------- $2

4 units – 2 ------ 3 units

1unit ------- 2

Total value of twenty-cent coins ------ 3 units ------ $6

Number of twenty-cent coins ------- 30 (600/20).

Another way is to use “SL” and work in a tabulated list.

20 cents: 50cents ------- 3:4 ------- 6:8

8 - 2 ------ 6, hence the condition is satisfied.

Total value of twenty-cent coins ------ 3 units ------ $6

Number of twenty-cent coins ------- 30 (600/20)

Best wishes[/quote]

Thank You!!!! :boogie: :rahrah:

[i_am_not_a_parent]

:lovesite: :thankyou: :udawoman: or :udaman:

Thanks to everyone!!

[zanen]

help ls Two cars race around a circular track at constant speeds starting at the same point. If they travel in opposite directions, then they meet every 30 seconds. If they travel in the same direction, then they meet every two minutes. If the track is 1800m long,what is the speed of each car?

[tianzhu]

zanen:

help ls Two cars race around a circular track at constant speeds starting at the same point. If they travel in opposite directions, then they meet every 30 seconds. If they travel in the same direction, then they meet every two minutes. If the track is 1800m long,what is the speed of each car?

Hi

Could you share with us where you take this question from?

Is this a PSLE type of question?

The answers to your question are 22.5m/s and 37.5m/s.

Best wishes

[enoawng]

tianzhu:

Hi

Could you share with us where you take this question from?

Is this a PSLE type of question?

The answers to your question are 22.5m/s and 37.5m/s.

Best wishes

Correct!

[MathIzzzFun]

zanen:

help ls Two cars race around a circular track at constant speeds starting at the same point. If they travel in opposite directions, then they meet every 30 seconds. If they travel in the same direction, then they meet every two minutes. If the track is 1800m long,what is the speed of each car?

Speed of faster car --> A
SPeed of slower car --> B
If they travel in opposite directions, then they meet every 30 seconds
-->total distance travelled in 30s = 1800m
so, A + B = 1800/30 m/s = 60m/s

If they travel in the same direction, then they meet every two minutes
--> faster car covers 1800m more than slower car in 2 min
ie A-B 1800/120 = 15m/s

A--> (60+15)/2 = 37.5 m/s
B--> 60-37.5 = 22.5 m/s

cheers.

[jjxy mum]

tianzhu:

jjxy mum:

Hi,

Thank you for your reply, we are still quite confused on the Cynthia's portion.

Hi

Ok, managed to find the pictorial, hope this helps.

Best wishes

http://farm9.staticflickr.com/8155/7674972602_fac8ddb8c5_z.jpg\">

Hi,

Thank you very much. Finally, we understand it now.

[Essential]

Hi Tian Zhu thank you for your help for earlier question. One more question from Nanyang Prelim 2012. Q13. both shops. ABC and XYZ , offered a 15% discount for the same type of mattress. If Mr Muthu were to buy from shop XYZ ,he would have paid $38.25 less than the discounted price in shop ABC. a) What was the discounted price in the shop ABC ?

b) the original price of the mattress in Shop ABC was $1510. what was the minimum percentage discount it must offer so that the discounted price in shop ABC would be lower than the discounted price in Shop XYZ? Give your answer connect to the nearest percent.Thankyou in adv