Q&A - PSLE Math

[corneyAmber]

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[Vanilla Cake]

musette:

A car and a coach travelled from Town A and Town B. The coach left Town A at 0648 and it took 5 hours to reach Town B. The car started 30 minutes later than the coach and it took 4 hours to reach Town B. At what time did the car catch up to the coach?

Constant distance
Ratio of time
Car : Coach
4 : 5

Ratio of speed
Car : Coach
5 : 4

Difference in speed = 1u
Since the coach left Town earlier by 1/2 hour, distance travelled = 1/2x4u=2u
Time taken for car to catch up for this distance = 2u/1u= 2 hours
Time for car to catch up with the coach -> Add 2 hours + 1/2 hour to 0648 = 0918

OR

Assume distance between Town A and Town B be D
Constant speed of coach = D/5 = 0.2D
Constant speed of car = D/4 = 0.25D
Difference in the constant speed of car and coach = 0.25D-0.2D=0.05D

Distance travelled by the coach in 1/2 hour earlier = 1/2x0.2D=0.1D
Time taken for car to catch up = 0.1D/0.05D= 2 hours

0648......+1/2h......+2h.............0918
The car caught up with the coach at 0918

OR

LCM of 4 and 5 is 20.Distance between the 2 towns are 20 units
Coach: 5 hours for 20 units ie 1 hour for 4 units
Car: 4 hours for 20 units ie 1 hour for 5 units

Comparing, car travelled 1 more unit than the coach in 1 hour .
Since the coach started 1/2 hour earlier, headstart = 1/2x4units = 2 units
So, the car needed to catch up with this 2 units that it lost.

Car caught up by a unit in 1 hour
2 units will need 2 hours
meaning the car needs 2 hours to catch up with the coach.

0648......+1/2h......+2h.............0918
The car caught up with the coach at 0918

OR

Refer to http://prischoolmaths.blogspot.com/2009/09/combined-hokkien-speed-question.html

[Dharma]

musette:

Hi,


Can somebody please show me the working for this question?

From Singapore Hokkien Huay Kuan schools, 2009 Prelim, Paper 2 Q15

A car and a coach travelled from Town A and Town B. The coach left Town A at 0648 and it took 5 hours to reach Town B. The car started 30 minutes later than the coach and it took 4 hours to reach Town B. At what time did the car catch up to the coach?

I just can't solve this without using algebra and simultaneous equations.

Thank you!

Time ratio => Coach : Car = 5:4
Speed ratio => Coach : Car = 4:5
Distance travelled by coach in 1/2hr
= 4u x 1/2
= 2u

Time taken for to catch up with coach
= 2u/(5u-4u)
= 2hrs

2 hrs after car left Town A
= 0918 or 9.18am

[Dharma]

liketoeat:

Hi, I don't know if this question is appropriate for P6 but my niece received it as her homework from her school teacher.


Toy Train A and Toy Train B are 15 m apart from each other. When the toy trains moved towards each other, they would meet in 5 min. However, if the toy trains moved in the same direction, toy Train A would overtake Toy Train B in 5/12 h. Find the speed of Toy Train A and Toy Train B.

Speed of train A + Speed of train B = 15m/5min = 3m/min
Speed of train A - Speed of train B = 15m/25min = 0.6m/min
Speed of train A = (3.6/2)m/min = 1.8m/min
Speed if train B = 1.2m/min

[musette]

Thank you VC and Dharma for the solution! Really appreciate it.

[liketoeat]

Thank you, Dharma…I’ll need some time to understand the solution.

[Dharma]

liketoeat:

Thank you, Dharma....I'll need some time to understand the solution.

Hi liketoeat,

Time reqd to meet = Distance apart/Sum of Speeds of trains

Time reqd to catch up = Distance apart/ Diff in Speeds of trains

[liketoeat]

Dharma:

liketoeat:

Thank you, Dharma....I'll need some time to understand the solution.

Hi liketoeat,

Time reqd to meet = Distance apart/Sum of Speeds of trains

Time reqd to catch up = Distance apart/ Diff in Speeds of trains

oh yes, got it. Thanks again.

[tianzhu]

Vanilla Cake:

Hope that other members can come forward with pictorial diagram to help you understand better.

Hi Vanilla Cake

Hope this may help.

To all dads in KSP, enjoy the cookies and have a happy and memorable Father’s Day.

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Best wishes.

[abc_parent]

Hi gurus !

Can anyone tell me for this particular question, why the solution for line 3 is so? Where is the area of circle in the question?

The diagram can be found here:
-> http://psle2010a.blogspot.com/search/label/M%20Circle%20P6%20RGS

----------------------------------------------------------------

1/2 x 3.14 x 4 x 4 = 25.12


33.5 – 25.12 = 8.38


3.14 x 8 x 8 = 200.96 (can someone explain this step?)


200.96 – 8.38 – 8.38 = 184.2 cm2 (can someone also explain this step?)