Q&A - PSLE Math

[tianzhu]

ozora:

Any solution to these 2 questions from Rosyths paper?

q1. Abdul , Bern and Chin were all standing in a straight line waiting for a race to start. Chin was 300m ahead of Bern and Bern was 100m ahead of Abdul. At 9 am, they started the race.Abdul overtook Bern in 5 mins and in another 5 mins, Abdul overtook Chin. If Bern's speed is 150m/min, at what time did Bern overtake Chin?

Hi

As in any question on “Speed”, it’s always useful to start with a simple diagram showing the relationship between the runners.Once done, things fall into places.

There are two ways to go about it.

Use the familiar Speed triangle learned in school.

Abdul and Bern
In 5 mins, Bern travelled (150*5) or 750m
In 5 mins, Abdul travelled (100+750) or 850m
Hence, Abdul’s speed is 850/5 or 170 m/min

Abdul and Chin
In 10 mins, Abdul travelled (170*10) or 1700m
Chin travelled (1700 - 400) or 1300m in 10 mins.
Chin’s speed is 130m/min

Bern and Chin
Difference between Bern and Chin’s speed ------- 20 m/min.
Chin was 300m ahead of Bern
300/20 ------ 15 mins

Bern overtook Chin at 9.15am

The second way, use “catch up”

Abdul and Bern
Head start ------ 100m
Time to catch up -------5 mins
Speed difference ------100/5 ------20

Abdul’s speed -------- 150+20 ------170m/min

Abdul and Chin
Head start ------ 400m
Time to catch up -------10 mins
Speed difference ------400/10 ------40

Chin’s speed -------- 170 - 40 ------130m/min

Bern and Chin
Head start ------ 300m
Speed difference ------ 20
Time to catch up ------- 300/20 ----- 15 mins

Bern overtook Chin at 9.15am

Best wishes

[MathIzzzFun]

ozora:

Any solution to these 2 questions from Rosyths paper?

q1. Abdul , Bern and Chin were all standing in a straight line waiting for a race to start. Chin was 300m ahead of Bern and Bern was 100m ahead of Abdul. At 9 am, they started the race.Abdul overtook Bern in 5 mins and in another 5 mins, Abdul overtook Chin. If Bern's speed is 150m/min, at what time did Bern overtake Chin?

q2. Alan had some sweets and chocolate. If he ate 1 sweet, the ratio of the number of sweets to the number of chocolate left in the bag would be 2:3.
If he ate 1 chocolate, the ratio of the number of sweets to the number of chocolate left in the bag would be 7:10. What was the ratio of the number of sweets to the number of chocolate he had in the bag ?

Hi

Q2 is a variation of the \"total unchanged\" type of questions - just remove the 1 from the total and work the question with initial ratio of 2:3 and final ratio of 7:10. And then add \"1\" back to the total..

If 1 sweet is removed,
Sweets : Chocolate = 2:3 (initial)

If 1 chocolate eaten (assume that now the 1 chocolate is replaced by 1 sweet), Sweets : Chocolate = 7:10 (final)

Make the initial total and final total the same...

Initially, Sweets : Chocolate = 2:3 = 34u : 51u
In the end, Sweets : Chocolate : 7 : 10 = 35u : 50u
So, 1u =1
Number of sweets = 35
Number of chocolates = 51

Ratio of sweets : chocolates = 35 : 51

cheers.

[Angel25]

Henry Park Prelim 2011 Q15.


Mr Lee packed some oranges into big boxes and apples into small boxed. Each big box contained 50 oranges and each small box contained 30 apples. After packing, there were 12 more big boxes than small boxes. Given that there were 1240 fewer apples than oranges, how many oranges were there ?

[ozora]

thanks tianzhu n MathIzzzFun

[Angel25]

Henry Park 2011 Prelim P2 Q11

[Angel25]

http://i53.tinypic.com/sfey6o.jpg\"> http://i53.tinypic.com/sfey6o.jpg\"> Henry Park 2011 Prelim P2 Q11

[Angel25]

http://i52.tinypic.com/10ruv0z.jpg\"> Henry Park 2011 Prelim P2 Q10

[Angel25]

CHIJ 2011 Prelims P2 Q15


Donavan, Ethan, Freddy and Gilbert shared some trading cards. Donavan recevived 20% of all the trading cards. Ethan received 48 fewer trading cards than Donavan. Freddy received twice as many trading cards as Ethan ans Gilbert received the remaining 432 trading cards.

a) Find the total number of trading cards shared by the 4 boys.
b)If Donavan was given additional trading cards, he would have a total of 487 trading cards. Find the percentage increase in the number of trading cards Donavan has.

[Angel25]

CHIJ Prelims 2011 P2 Q12


At 8.30am, Myke and Jerome set off at the same time from Town X to Town Y. At 11.00am, Myke completed his journey but Jerome had covered only 5/8 of the journey. Jerome’s speed was 54km/h slower than Myke’s.

a) Find the distance between Town X and Town Y.
b) At what time would Jerome complete his journey?

[Angel25]

Pei Chuan Public School Prelim 2011 P2 Q18


At first, Ella had $52 more than Felix. After Ella had spent 25% of her money and Felix had spent 3/5 of his, Ella had $123 more than Felix. How much money did Ella have at first?