## Q&A - PSLE Math

### Re: Q&A - PSLE Math

vvv

A: 1696145

Subject: {Math}

Level: {P6}

Tags: {Internal transfer, total same}

Source: {}

^^^

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

A: 1696145

Subject: {Math}

Level: {P6}

Tags: {Internal transfer, total same}

Source: {}

^^^

In the beginning,belnanna wrote:

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

### Re: Q&A - PSLE Math

vvv

A: 1696145

Subject: {Math}

Level: {P6}

Tags: {Speed}

Source: {}

^^^

A: 1696145

Subject: {Math}

Level: {P6}

Tags: {Speed}

Source: {}

^^^

belnanna wrote:

### Re: Q&A - PSLE Math

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.BigDevil wrote:vvv

A: 1696145

Subject: {Math}

Level: {P6}

Tags: {Speed}

Source: {}

^^^belnanna wrote:

I got the same answer as you, so I think the question is not set properly.

- alfretztay
- KiasuGrandMaster
**Posts:**1199**Joined:**Sun Sep 12,**Total Likes:**5

### Re: Q&A - PSLE Math

I would solve the above question as follows :Ender wrote: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.BigDevil wrote:vvv

A: 1696145

Subject: {Math}

Level: {P6}

Tags: {Speed}

Source: {}

^^^belnanna wrote:

I got the same answer as you, so I think the question is not set properly.

(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.

### Re: Q&A - PSLE Math

Ender wrote: 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.

Last edited by BigDevil on Fri Jul 08, 2016 10:04 am, edited 2 times in total.

### Re: Q&A - PSLE Math

Never do your checking huh?alfretztay wrote: 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.

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.

### Re: Q&A - PSLE Math

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.BigDevil wrote:Ender wrote: 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.

- alfretztay
- KiasuGrandMaster
**Posts:**1199**Joined:**Sun Sep 12,**Total Likes:**5

### Re: Q&A - PSLE Math

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.'

Last edited by alfretztay on Fri Jul 08, 2016 1:09 pm, edited 2 times in total.

- alfretztay
- KiasuGrandMaster
**Posts:**1199**Joined:**Sun Sep 12,**Total Likes:**5

### Re: Q&A - PSLE Math

alfretztay wrote:(6/60) x 75 = 7.5BigDevil wrote:Never do your checking huh?alfretztay wrote: 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.

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.

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.