Q&A - PSLE Math

[Brenda10]

Hi Tianzhu


Yes. You’re right.

She is spending most of her time on reading or playing those Mystery game since not much work from school. I do wish your judgment is correct.

Thank you and have a nice day. :lol:

[Maths Monster]

ksmama:

Ann is driving to a destination. If she travels at 80km/h, she would be 20min late. If she travels at 60km/h, she would be 45 min late. How long will journey take if she travels at 90km/h.


For your help. Thnx!

Since distance is the same, the ratio of speed is inverse to the ratio of time taken:

Ratio of speed
80km/h : 60km/h
4 : 3

Ratio of time taken
3 : 4

1 part => 45 - 20 = 25 mins

Time taken for speed of 80km/h = 3 x 25 = 75 mins
Time taken for speed of 60km/h = 4 x 25 = 100 mins

Distance = 80 x 75 / 60 = 100km

Therefore, time taken if speed is 90km/h is = 100 / 90 = 1 1/9h

Check:
To be on time, she must reach the destination in 75 - 20 = 55mins
If speed is 60km/h, she will late by 100 - 55 = 45 mins

[tianzhu]

Hi ksmama


From going through with my boy last year, I realised that the formula, Distance = Speed*Time is commonly used to solve questions on Speed in P6.

I’ll share three ways to solve your question. Generally, P6 students should be familiar with the first two methods. The last method uses the concept of inverse proportion.This means that as one quantity becomes smaller, the other becomes larger.This should be covered in secondary Maths. But, I understand, they are taught to selected groups of P6 students in schools.Students who attend enrichment classes may also be exposed to this concept.

It’s good to expose kids to different solutions and let them choose the method they are most comfortable with.

I hope you will find them useful.

Best wishes

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[liketoeat]

tianzhu:

Hi


This question touches on distances moved by the tips of the hour and minute hands. It refers to distance moved along the circumference of a circle (arc).

In half an hour, the minute hand moves 180 degrees.
In half an hour, the hour hand goes through 15 degrees.

Distance moved by tip of hour hand is 15/360 * 2πr, where r is the length of the hour hand. ------ 1/12 πr

Distance moved by tip of minute hand is 180/360 * 2π (3r), where 3r is the length of the minute hand. ------- 3πr

Therefore, the answer is 36:1

(Sorry, pi appears as π when I transferred the text from Words 2007 to this thread)

Best wishes

Thank you, Tianzhu.

[tianzhu]

liketoeat:

Thank you, Tianzhu.

Hi liketoeat

You're welcome.

Best wishes

[tianzhu]

Hi


This is an interesting question from the cbox.

Mrs Lim bought some bowls and plates.If she buys another 5 bowls,there are 60% as many bowls as plates.If she buys another 9 plates,there will be thrice as many plates as bowls.How many bowls did she buy?

Best wishes

[Maths Monster]

tianzhu:

Hi


This is an interesting question from the cbox.

Mrs Lim bought some bowls and plates.If she buys another 5 bowls,there are 60% as many bowls as plates.If she buys another 9 plates,there will be thrice as many plates as bowls.How many bowls did she buy?

Best wishes

If she buys another 5 bowls,there are 60% as many bowls as plates.
Let 6u be the number of bowls, then
B [6u]
P [10u]

At start,
B [6u - 5]
P [10u]

If she buys another 9 plates,there will be thrice as many plates as bowls.
B [6u - 5]
P [10u + 9]

We can write the equation as:
(6u - 5) x 3 = (10u + 9)
18u -15 = 10u + 9
8u = 24
u = 3

Therefore at start,
Bowls = 6u - 5 = 13
Plates = 10u = 30

Check:
If she buys another 5 bowls,there are 60% as many bowls as plates.
B = 6u = 18
P = 10u = 30
=> B is 18/30 x 100% = 60% of P

If she buys another 9 plates,there will be thrice as many plates as bowls.
B = 6u - 5 = 13
P = 10u + 9 = 39
=> P is 39/13 = 3 times of B

[kancheongmum]

hi all


appreciate help for this question
P6 Hokkien HK prelim paper Q15
a car n a coach travelled from town A to town B. The coach left Town A at 0648 and it took 5 hrs to reach Town B. The car started 30 mins later than the coach and it took 4 hours to reach Town B. At what time did the car catch up with the coach? (ANS 0918)

I have seen the answer somewhere but don’t understand so can’t explain to my son.

Thanks!

[RRMummy]

hi kancheongmum,


the thread below is super helpful in solving maths questions. I would suggest you post your future questions there too.

http://www.kiasuparents.com/kiasu/forum/viewtopic.php?t=6373&start=1890

Mods pls merge.

[kancheongmum]

hi rrmummy thanks for the reply. I know of this thread but hit the wrong button and I start a new thread. Take this opportunity the thanks all parents and teachers who are willing to spend time to answer all the questions even the most challenging ones.