Q&A - PSLE Math

[belnanna]

Thank you!

[BigDevil]

vvv
A: 1696145
Subject: {Math}
Level: {P6}
Tags: {Internal transfer, total same}
Source: {}
^^^

In the beginning,
S -> 100u ribbons
L -> 100p buttons

After transfer,
S -> 20u ribbons, 10p butttons
L -> 80u ribbons, 90p buttons

20% of Shyamala's collections were ribbons
20u -> 20%
10p -> 80%
10p = 80u

Lily had 480 more buttons than ribbons
90p - 80u = 480
90p - 10p = 480
80p = 480
1p = 6

Lily had 100 x 6 = 600 buttons at first

[BigDevil]

vvv
A: 1696145
Subject: {Math}
Level: {P6}
Tags: {Speed}
Source: {}
^^^

[Ender]

vvv
A: 1696145
Subject: {Math}
Level: {P6}
Tags: {Speed}
Source: {}
^^^

Peter travels at 30km/h, and Dave travels at 70km/h. Although they set off at the same time and traveled the same distance, Peter, who is slower, arrived at his destination earlier.
I got the same answer as you, so I think the question is not set properly.

[alfretztay]

vvv
A: 1696145
Subject: {Math}
Level: {P6}
Tags: {Speed}
Source: {}
^^^

Peter travels at 30km/h, and Dave travels at 70km/h. Although they set off at the same time and traveled the same distance, Peter, who is slower, arrived at his destination earlier.
I got the same answer as you, so I think the question is not set properly.

I would solve the above question as follows :
(a)

24 - 6 = 18 (Both took 18 min to pass each other)

(18/60) x 70 = 21 (Dave had travelled 21km in 18min before he passed by Peter)


(b)

6 minutes after they had passed each other, Dave was still 2 km away from Town B.

(6/60) x 70 = 7 (Dave travelled another 7km in the next 6min)

2 + 7 + 21 = 30 (total distance was 30km)

30/(24/60) = 75


Ans : (a) 21km; (b) 75km/h.

[BigDevil]

Peter travels at 30km/h, and Dave travels at 70km/h. Although they set off at the same time and traveled the same distance, Peter, who is slower, arrived at his destination earlier.
I got the same answer as you, so I think the question is not set properly.

I was also thrown off by the statement "At the same time, Peter drove from
Town B to Town A", making me assume that they started off at the exact
same time.

But the final answer does not make sense, so I had to re-work from
the time they passed each other to arrive at the answer above.

[BigDevil]

I would solve the above question as follows :
(a)

24 - 6 = 18 (Both took 18 min to pass each other)

(18/60) x 70 = 21 (Dave had travelled 21km in 18min before he passed by Peter)


(b)

6 minutes after they had passed each other, Dave was still 2 km away from Town B.

(6/60) x 70 = 7 (Dave travelled another 7km in the next 6min)

2 + 7 + 21 = 30 (total distance was 30km)

30/(24/60) = 75


Ans : (a) 21km; (b) 75km/h.

Never do your checking huh?

This was the answer I got when I assumed that both started their
travel at the same time.

So if Peter traveled from B to A at 75km/h, and he took
18mins to pass Dave, he would have traveled
(18/60) x 75 = 22.5km

But you also said Dave traveled 21km before passing Peter.
22.5 + 21 = 43.5km total distance....which is not the same as the 30km you worked out.

[Ender]

Peter travels at 30km/h, and Dave travels at 70km/h. Although they set off at the same time and traveled the same distance, Peter, who is slower, arrived at his destination earlier.
I got the same answer as you, so I think the question is not set properly.

I was also thrown off by the statement "At the same time, Peter drove from
Town B to Town A", making me assume that they started off at the exact
same time.

But the final answer does not make sense, so I had to re-work from
the time they passed each other to arrive at the answer above.

Whether start from mid point or from the 18mins peter traveled to mid point, everything just don't adds up. It would be a pity if this type of sub standard question appears in the PSLE. The bright students who are able to spot the anomaly would be stuck, while those whose answer matched the flawed model answer will get the points.

[alfretztay]

I would use the 'the lesser of two evils principle or lesser evil principle, which is the principle that when faced with selecting from two unpleasant options, the one which is least harmful should be chosen.'

[alfretztay]

I would solve the above question as follows :
(a)

24 - 6 = 18 (Both took 18 min to pass each other)

(18/60) x 70 = 21 (Dave had travelled 21km in 18min before he passed by Peter)


(b)

6 minutes after they had passed each other, Dave was still 2 km away from Town B.

(6/60) x 70 = 7 (Dave travelled another 7km in the next 6min)

2 + 7 + 21 = 30 (total distance was 30km)

30/(24/60) = 75


Ans : (a) 21km; (b) 75km/h.

Never do your checking huh?

This was the answer I got when I assumed that both started their
travel at the same time.

So if Peter traveled from B to A at 75km/h, and he took
18mins to pass Dave, he would have traveled
(18/60) x 75 = 22.5km

But you also said Dave traveled 21km before passing Peter.
22.5 + 21 = 43.5km total distance....which is not the same as the 30km you worked out.

(6/60) x 75 = 7.5
7.5 + 22.5 = 30

I do concur that the question is flawed but when students are faced with it, they have to do their best to solve it, don't they? I too believe that only the one who set the question should, if not will, know it all.