Q&A - PSLE Math

[balu_priya]

MathIzzzFun:

balu_priya:

My friend who is too shy to post asked me to help her to post on ksp.

Would appreciate help on the following questions:

1.Sam is 5times as old as his sister. iN 10 yrs time Sam will be 12 yrss less than thrice his sisters age then. How much older is Sam than his sister?

Age now,
Sam's sister --> 1 unit
Sam --> 5 units

10 years' time,
Sam's sister --> 1 unit + 10 -- \"thrice\" --> 3 units + 30
Sam --> 5 units + 10

Sam is 12 years less than his sister:
5 units+ 10+12 = 3 units + 30
1 unit --> 4

4 units --> 16

Sam is 16 years older than his sister.

cheers.

:thankyou:

[Michaelia0816]

Tianzhu,

Pls help,

1)Each of the three cards shown below is printed with a different whole number.
The biggest number is 42. When these number are added two at a time, the sums are 57,64 and 77. What are the other 2 numbers?

2) A forty- page newspaper, which consists of only one section, has a sheet with page 9 and page 10 missing. What other pages are missing?

Pls done it by today as I am going to have math prelim the next day~.~

[MathIzzzFun]

Petkwang:

Belle, Cathy and Denise had a collection of stickers. Cathy and Denise collected 7/10 of the stickers, Belle and Denise collected 6/7 of the stickers, Belle and Cathy collected 620 stickers altogehter. How many more stickers did Denise collected than Belle? Answer 360 stickers


Lily is meeting a friend at a certain time. If she drive 80km/h she will be 1/3 hr late. If she drive at 60km/h, she will be 3/4 hr late. How long will be the journey take if she drive at 90km/h? Answer 1 1/9 hr
Thank you in advance.

Q1.
Total -> 70 units
C+D -> 49 units
B --> 70 unit s- 49 units = 21 units

B+D -> 60 units
C --> 70 units – 60 units = 10 units
D --> 60 units – 21 units = 39 units

B --> 21 units, C --> 10 units, D --> 39 units
B+C --> 31 units = 620
1 unit --> 20
39 units – 21 units = 18 units
18 x 20 = 360

Denise collected 360 stickers more than Belle.


Q2.
Ratio of speed at 80 km/h : 60 km/h = 4 : 3
Ratio of time taken to travel same distance at 80 km/h : 60 km/h = 3u : 4u

¾ h – ⅓ h = 5/12 h = 25 min -> travelling at 80km/h is 25 min faster than travelling same distance at 60 km/h

1u -> 25 min, total time taken at 60 km/h
--> 4 x 25 min = 100 min = 2 ⅔ h
Total time taken at 90 km/h = 60/90 x 2 ⅔ h = 10/9 h = 1¹∕₉ h

cheers.

[tianzhu]

Michaelia0816:

Tianzhu,

Pls help,

1)Each of the three cards shown below is printed with a different whole number.
The biggest number is 42. When these number are added two at a time, the sums are 57,64 and 77. What are the other 2 numbers?

Hi

Hope this helps.

Best wishes

http://farm9.staticflickr.com/8440/7836643020_0af55760ca_z.jpg\">

[2DMommy]

Please help me with these :


Find the sum of 35 + 37 + 39 + 41 + 43 … + 231 + 233.

What is the short cut to this question ?

Thank you.

[superksmum]

Hi please help on this question (Henry Park Prelim 2011, question 16).


Mr Lee took 7 hours to travel from Town A to Town B while Mr Wong took 8 hours to travel from Town B to Town A. Both of them did not change their spped throughout the journey. Both of them started off at the same time and moved towards each other. 3 hours later, they were 110km apart. What was the speed Mr Lee was driving?

Thank you.

[whitety]

Hi, need help on this qn.


Every Sat, Mabel will go for her usual exercise. If she runs up 32 steps and walks up 68 steps, she will take 184 seconds. If she runs up 50 steps and walks 50 steps, she will take 175 seconds. If she runs at the same rate throughout the whole exercise, how long will she take to run the 100 steps?


Thanks!

[jonaandr]

please help to solve the below 2 questions.


1. There were some balls in Boxes A,B and C. For every 3 balls in Box A, there were 7 balls in Box. For every 5 balls in Box B, there were 6 balls in Box C. After 48 balls were transferred from Box C to Box A, the ratio of the number of balls in Box A to the number of ball in Box B to the number of balls in Box C became 19:35:38. Find the total number of balls in the three boxes.

2. A motorcyclist travelle from Town A to Town B. It passed a taxi travelling from Town B to Town A. The taxi was traveling at a speed of 90 km/h. The motorcyclist reached Town B 1 1/2 hours after passing the taxi but the taxi was still 25 km away from Twon A. Both the motorcyclist and the taxi did not change their speeds throughout their journeys. If the motorcyclist took 4 hours to complete the shole journey, what was the distance between the two towns?

Thanks!

[charsen]

superksmum:

Hi please help on this question (Henry Park Prelim 2011, question 16).


Mr Lee took 7 hours to travel from Town A to Town B while Mr Wong took 8 hours to travel from Town B to Town A. Both of them did not change their spped throughout the journey. Both of them started off at the same time and moved towards each other. 3 hours later, they were 110km apart. What was the speed Mr Lee was driving?

Thank you.

Hi
In 3 hours, lee drove 3/8 of the journey.At the same time,wong took 3/7 of the journey.So,we should make the denominators 8 and 7 to be 56 since the distance in both is common.

Lee travelled 24U and wong travelled 21U.
56u-24U-21U=11U
11U-110km
1U-110/11=10km
Distance lee travelled--->10x24=240km
Lee's speed------>240/3=80km/h(ANS)

[charsen]

jonaandr:

please help to solve the below 2 questions.


1. There were some balls in Boxes A,B and C. For every 3 balls in Box A, there were 7 balls in Box. For every 5 balls in Box B, there were 6 balls in Box C. After 48 balls were transferred from Box C to Box A, the ratio of the number of balls in Box A to the number of ball in Box B to the number of balls in Box C became 19:35:38. Find the total number of balls in the three boxes.

2. A motorcyclist travelled from Town A to Town B. It passed a taxi travelling from Town B to Town A. The taxi was traveling at a speed of 90 km/h. The motorcyclist reached Town B 1 1/2 hours after passing the taxi but the taxi was still 25 km away from Town A. Both the motorcyclist and the taxi did not change their speeds throughout their journeys. If the motorcyclist took 4 hours to complete the shole journey, what was the distance between the two towns?

Thanks!

Hi
Q1. A:B B:C
3:7 5:6
x5 x5 x7 x7
A:B:C
15:35:42
19u-15u=4u
4u=48
1u=48/4=12
Total no. of Units----->92U-12x92=1104 balls (ANS)

Q2.Distance between meeting point and town A--->(90x 3/2)+25=135+25
=160km Time taken for the motorcyclist from town a to meeting point-->4h-1 1/2h
=2 1/2 h
Speed of the motorcyclist---->160/2 1/2h=64km/h
Distance between town A and town B------>64x4=256km(Ans)
cheers.