Q&A - PSLE Math

[Oracle]

Thanks a lot MathIzzzFun and SpeedMaths (still up at 1:54am!!! Phew …)

Will show them to my daughter tonight and see if she is able to relate.

The other two questions:

Q4. Jeremy walks to school at an average speed of 4 km/h everyday. One day, after walking a distance of 1 km, he realised that his watch was slow. So he ran at a constant speed and managed to reach school just on time. Later, he calculated that if he had run at this speed right from the start of the journey, he would have reached school 5 minutes earlier. What was his running speed?

Q5. Mr Tan took 6 hours to travel from Town A to Town B. Mr Lim took 4 hours to travel from Town B to Town A. If both of them started travelling at 10 am, at what time did they pass each other?

Thank you.

[MathIzzzFun]

Oracle:

Thanks a lot MathIzzzFun and SpeedMaths (still up at 1:54am!!! Phew ...)

Will show them to my daughter tonight and see if she is able to relate.

The other two questions:

Q4. Jeremy walks to school at an average speed of 4 km/h everyday. One day, after walking a distance of 1 km, he realised that his watch was slow. So he ran at a constant speed and managed to reach school just on time. Later, he calculated that if he had run at this speed right from the start of the journey, he would have reached school 5 minutes earlier. What was his running speed?


Thank you.

For questions on speed, it is always good to draw a diagram ...



<-----------1 km ----------->
Home _____walk________X __________RUN_____________ School

Home _____RUN________X __________RUN_____________ School

Supposed Jeremy started running from point X which is 1 km from his house, we see that the time saved (5 minutes faster) if he had started running from the start is from running the first 1 km versus walking the first 1 km.

Time taken to walk 1 km = 1/4 h = 15 min
Time taken to run 1 km = 15 min - 5 min = 10 min

Jeremy's running speed = 1 km/ 10 min = 6 km/h

cheers.

[Oldschool]

Oracle:

Will show them to my daughter tonight and see if she is able to relate.

Hi,

There is an old article on speed by another forum user, which may offer some direction.

http://www.kiasuparents.com/kiasu/content/psle-math-tips-speed-questions

Other insight on speed, which you may find helpful, is also posted in this forum.

http://www.kiasuparents.com/kiasu/forum/viewtopic.php?p=976873#p976873

Regards

[MathIzzzFun]

Oracle:

Thanks a lot MathIzzzFun and SpeedMaths (still up at 1:54am!!! Phew ...)

Will show them to my daughter tonight and see if she is able to relate.

The other two questions:


Q5. Mr Tan took 6 hours to travel from Town A to Town B. Mr Lim took 4 hours to travel from Town B to Town A. If both of them started travelling at 10 am, at what time did they pass each other?

Thank you.

Time taken to travel the distance between A and B,
Mr Tan's time : Mr Lim's time = 6 : 4 = 3 : 2

Mr Tan's speed : Mr Lim's speed --> 2 : 3

When Mr Tan and Mr Lim passed each other,
Mr Tan has travelled 2 units from Town A, and
Mr Lim has travelled 3 units from Town B

Total distance between Town A and B = 2 units + 3 units = 5 units

Time taken for Mr Tan to travel 2 units = 2/5 x 6 h = 2.4h = 2h 24 min

10 am + 2h 24 min ---> 12.24pm

Mr Tan and Mr Lim passed each other at 12.24pm

cheers.

[Mary Joy]

Pls help me with this circle question…


two wheels with centres A and B are 641 cm apart.The radius of the small wheel is 7 cm.The ratio of the radius of the small wheel to the ratio of the big wheel is 1:3.Both the wheels are rolled in the inward direction until the centres are 113 cm apart. The two wheels need to make the same no of revolutions.

How many revolutions does each wheel make assuming that each wheel must make a complete revolution? (take pi:3.14)

[iCreative Math]

Radius of small wheel = 7 cm

Radius of big wheel = 21 cm (given ratio of 1:3)

In one complete revolution each, the small and big wheels would have travelled a combined distance of 2 X 3.14 X 28 = 175.84

For the centre to be 113 cm apart, the total distance travelled would have to be 641 - 113 = 528 cm.

The wheel would have each make 528 / 175.84 = 3 complete revolutions each.


Regards.
iCreative Math

[Easy-going]

can anyone help me with this problem sum please?

The ratio of the number of red markers to the number of blue markers in Box ia 3:1. The ratio of the number of red markers to the number of blue markers i Box B is 2:3. There are twice as many markers in Box than Box B.
A) What is the ratio of the number of red markers in Box A to the number of red markers in Box B?

B) 60 red markers are added into Box B and the ratio of the number of red markers to the number of blue markers in Box B becomes 4:1. How many blue markers are there in Box B?

Thanks in Advance

[PapayaDad]

B)

Red = 2u ; Blue = 3u
At first 2u:3u
Change +60 : 0
In the end 4p:1p
So
2u+60.....4p
3u.....1p
Make the part the same
2u+60.....4p
12u....4p
12u = 2u+60
u=6
Blue = 3u = 18

See http://www.kiasuparents.com/kiasu/content/math-questions-involving-two-changed-quantities

[PapayaDad]

can anyone help me with this problem sum please?

The ratio of the number of red markers to the number of blue markers in Box ia 3:1. The ratio of the number of red markers to the number of blue markers i Box B is 2:3. There are twice as many markers in Box than Box B.
A) What is the ratio of the number of red markers in Box A to the number of red markers in Box B?

Box A:
r=3u
b=1u
Total = 4u

Box B:
r=2p
b=3p
Total = 5p

There are twice as many markers in Box A than Box B. So
4u = 5p x 2 = 10p
u=2.5p

In Box A:
r=3u so r=3 x 2.5p = 7.5p

In Box B:
r=2p

Ratio is 7.5 to 2 or 15:4

[Oracle]

Thanks oldschool for the lead. The materials are informative indeed.


MathIzzzFun, re Ann and Ben question, may I know how you derived 1 unit ~ 24km?