Q&A - PSLE Math

[Dharma]

firebird:

Dear mathsguru


Good morning

Please help me on the following P6 Speed math:

A Van left Port Penang for Town Lalu at 9 a.m. A Car started its journey along the same route as the Van from starting point, two hours later. The car overtook the Van at 3 p.m. The speed of the car was 30 Km/h higher than Van. The Van took 7 hours to reach Town Lalu. Find the distance between Port Penang and Town Lalu.

The answer given was:

a) The speed of the car was 30 km/h more than the speed of the Van.
So 1hr = 30 km
4hr = 4 X 30 = 120 Km

I can understand this. Reason is 4 hours = (11am - 3 pm)


b) Distance travelled from Port Penang to Town Lalu
2 hours = 120 Km
7 hours = 120/2 X 7 = 420 Km (which is the answer given)

I really do not understand how 2 hours is linked to 120 km

Please help me as to how 2 hours is linked to 120 km.
Are there different method/steps/explaination available ?

Thank you
Firebird

For fixed distance (from Port Penang to the point where car overtakes van);

Time ratio => Van: Car = 3:2
Speed ratio => Van: Car = 2:3

3u – 2u = 30
Speed of van = 60km/h

Distance between Port Penang & Town Lalu = 60km/h x 7hrs = 420km

[adhdadhd]

firebird:

Dear Maths Guru


A Van left Port Penang for Town Lalu at 9.30 a.m. A car started its journey along the same express way two hours later. The car overtook the Van at 3 p.m. The speed of the car was 30 km/h greater than that of Van. The Van took 7 hour to reach Town Lalu. Find the distance between Port Penang and Town Lalu.

Firebird

9.30 am to 11.30 am, Car started 2 hours later than Van.
Average Speed of Van = V, Average Speed of Car = C, in km/h.
so, V=C-30

Key to note: Car and Van started at different time, but covered same distant when car overtake the van.
van 9.30am to 3 pm = 5.5 hrs, and Car 11.30 am to 3 pm = 3.5 hrs

Distant = Speed x time taken

5.5 x V = 3.5 x C
5.5 x V = 3.5 x (V+30)
2 V = 30 x 3.5 = 105
V= 52.5 (km/h)

The distant that the van covered = 52.5 x 7 = 367.5km.

[Suz855]

Alan, Benny, Clement and Danny had 105 marbles. Alan lost 3 marbles and Danny lost half of what he had. Benny's sister gave Benny another 6 marbles. Clement's aunt rewarded Clement by doubling what he had originally. In the end, the 4 boys had an equal number of marbles. How many more marbles than Danny did Alan have at first?


Is the qn looking for a comparison between Alan at first with Danny after he lost half of his marbles? Based on the qn, Danny should have more marbles than Alan at first, thanks

:?

[Tnsp]

http://www.postimage.org/image.php?v=aVS8f8S


The question is simply asking the student to solve for A, B, C and D, the number of marbles they had at first.

Danny definitely had more marbles than Alan. Danny had 48 while Alan had 27.

I think is not meaningful to ask Danny (after he lost half) 24, compared to Alan (at first) 27.

It is the way the question was written. I don't like it either, because it is very awkard. The English department teachers should help the Maths department teachers to check the question papers before they use it.

[firebird]

Dear Tianhu


Good afternoon.

The question and working posted by me on speed was from an assessment book.

I also thank Dharma for the clear solution.

With best regards
Firebird

[firebird]

Dear adhdadhd


Thank you for the solution.

With best regards
firebird

[Joy]

Hi All,


Good morning.

Below is a math question from my dd, p5 sa1 exam.I also noticed similar question came out in another school for p6 sa1 this year.

Just wonder, anyone has seen similar question before?If yes, kindly advice where is the source?

Mdm Lek had 57 apples and oranges altogether.There were 3 fewer oranges than apples.She gave away half as many oranges as apples to her neighbours.vShe was left with twice as many oranges as apples.How many apples did she give away?

thank you.Regards
Joy

[CoffeeCat]

Joy:

Hi All,


Good morning.

Below is a math question from my dd, p5 sa1 exam.I also noticed similar question came out in another school for p6 sa1 this year.

Just wonder, anyone has seen similar question before?If yes, kindly advice where is the source?

Theoretically this is not a very challenging problem. The concept tested is the \"more than/less than\" concepts as exemplified by books like onsponge or challenging maths problems made easy. I dun think you will find a exact similar question there.

Anyway I know this looks like or will remind people of another type of challenging problem sums called external transfer (could this be the one that you saw and very interested in?)
external transfer questions are usually more challenging because the exact quantities are not told (we know the number of apples and oranges in this question), only the ratios are given.

[Joy]

thanks.


Was trying to find out cos has never seen such question while practising the past year school papers.

Will take a look at the book that u mention.Thank you.

rgds
Joy

CoffeeCat:

Joy:

Hi All,

Good morning.

Below is a math question from my dd, p5 sa1 exam.I also noticed similar question came out in another school for p6 sa1 this year.

Just wonder, anyone has seen similar question before?If yes, kindly advice where is the source?

Theoretically this is not a very challenging problem. The concept tested is the \"more than/less than\" concepts as exemplified by books like onsponge or challenging maths problems made easy. I dun think you will find a exact similar question there.

Anyway I know this looks like or will remind people of another type of challenging problem sums called external transfer (could this be the one that you saw and very interested in?)
external transfer questions are usually more challenging because the exact quantities are not told (we know the number of apples and oranges in this question), only the ratios are given.

[atutor2001]

Joy:

Hi All,


Good morning.

Below is a math question from my dd, p5 sa1 exam.I also noticed similar question came out in another school for p6 sa1 this year.

Just wonder, anyone has seen similar question before?If yes, kindly advice where is the source?

Mdm Lek had 57 apples and oranges altogether.There were 3 fewer oranges than apples.She gave away half as many oranges as apples to her neighbours.vShe was left with twice as many oranges as apples.How many apples did she give away?

thank you.Regards
Joy

Hi Joy

This type of question can be found in many exam papers. The characteristic of such question is that the examiner has added one more working step by giving the actual number of apples and oranges \"indirectly\" - i.e. from the total of 57 and the difference of 3, students can find the actual no. of apples and oranges.

This additional working step can be incorporated into all kinds of questions involving 2 quantities but will usually leave students totally confused. I remembered telling my kids to specially look out for information given in this way (i.e. total with difference).