Q&A - PSLE Math

[Michaelia0816]

Thanks, the shadow snake, for your time to help to solve!

[charsen]

dicoyote:

hi, am not able to identify the model to use for this question, thus seeking help, thanks in advanced


A shopkeeper had some blue and red pens in his book shop. There were twice as many red pens as blue pens. The shopkeeper sold the pens in bundles of 2 red pens and 3 blue pens. After selling all the blue pens, he still had 120 red pens left. How many pens did he have in his bookshop at first?

Hi,
This Question is a two ratio problem and could be solved by cross multipication.
First,You subtract 120 from 2U.The 2U refers to the red pen at first.I am doing this so that the ratio of the pens at first is equal to the Selling ratio , which is 2:3.
If you cross multiply now,
(2U-120)x3=6U-360
6U-360=(2x1)u
4U=360
1U=360/4=90
no.of pens at first-3U-90x3=270(ans)
cheers

[Michaelia0816]

Am I right?, Tianzhu?

[MathIzzzFun]

dicoyote:

hi, am not able to identify the model to use for this question, thus seeking help, thanks in advanced


A shopkeeper had some blue and red pens in his book shop. There were twice as many red pens as blue pens. The shopkeeper sold the pens in bundles of 2 red pens and 3 blue pens. After selling all the blue pens, he still had 120 red pens left. How many pens did he have in his bookshop at first?

Hi

note that the number of blue pens sold = total number of blue pens

At first,
Red pens : Blue pens = 2 : 1 --> 6u : 3u -- total number of pens --> 9u
Sold,
Red pens : Blue pens --> 2u : 3u
Number of red pens left --> 4u = 120, 1u --> 30
Total number of red & blue pens at first = 9 x 30 = 270.

cheers.

[MathIzzzFun]

2632parent:

Need help on this question, just cannot get the answer?


1) Mr Wu and Mr Zheng travelled along the same expressway to Town M. Mr Wu left his flat at 6.20am and travelled at 90km/h. 40 minutes later, Mr Zheng left for Town M and drove at an average speed of 105 km/h. At what time did they meet on the way?

Thank you

Hi

Using speed/time ratio,

Mr Wu's speed : Mr Zheng's speed = 90 : 105 = 6u : 7u
When they meet on the way, time taken by Mr Wu : Mr Zheng --> 7u : 6u
1u --> 40 min
7 x 40 = 280 min = 4h 40 min
6.20am + 4h 40min --> 11am
They met at 11am
------------------------------
alternatively, you can also use the difference in speed to work out the time they will meet.

When Mr Zheng left for Town M, Mr Wu would have travelled 40 min x 90km/h = 60 km

105 km/h - 90 km/h = 15 km/h --> Mr Zheng would catch up 15 km every hour

60 /15 = 4h --> Mr Zheng caught up with Mr Wu after 4h
6.20am + 40 min + 4h --> 11 am

They met at 11 am

cheers.

[elkniwt]

Hello,


Need help in this qn from Henry Park 2011 Prelim :

http://i48.tinypic.com/2i7qozm.jpg\">

Thanks!!

[tianzhu]

Michaelia0816:

Am I right?, Tianzhu?

Hi

This question has been discussed before.

You may use UM or MD.

I’ll give you some pointers.

Use 40 units.

Chocolate cookies (sold) -------- 25 units (5/6 of 30 units)

Chocolate cookies left ------- 5 units

1/5 of cookies left ------- 1/5*40 -------8 units

Almond cookies left ------- 8-5 ------ 3 units

Almond cookies sold ------ 10-3 ------ 7 units

Almond cookies sold ------- 210

7 units ------ 210

1 unit ------- 30

32*30 ------- 960(number of cookies sold)

Best wishes

[tianzhu]

Michaelia0816:

Pls help with this question too,


http://t.co/gPLtRATI, sorry to trouble you again!

Hi

Square Q is 4 times square P.

Square ----- 4 units

Square P ----- 1 unit

Each rectangle ------- 2 units

Fraction of black squares in fig 1 ------ 5/9

Area of floor covered by black squares ----- 5/9*(18*18) ------- 180

Best wishes

[dora miscq]

Mr and Mrs Leong left their house at the same time but travel in opposite directions.

Mr Leong travelled towards Bedok while Mrs Leong headed for Kallang.
Mrs Leong drove at a speed which was 10 km/h slower than Mr Leong.
30 minutes later, when Mr Leong reached Bedok, they were 95km apart.
How far did Mrs Leong travel when Mr Leong reached Bedok?

[tianzhu]

2DMommy:

2) Tom bought some chocolates and gave half of them to John. John bought some swees and gave half of them to Tom. Tom ate 12 sweets and John ate 18 chocolates. After that, the number of sweets and chocolates Tom had were in the ratio 1:7 and the number of swees and chocolates John had were in the ratio 1:4. How many sweets did John buy ?

Hi

A similar question has been discussed before.

The answer to your question is 68.

Hope this helps.

Best wishes

http://farm7.staticflickr.com/6188/6119123632_b0a9875903_z.jpg\">