Q&A - PSLE Math

[tianzhu]

Shimmer:

Q2. CYTHNIA walked to the library from school and at the same time, Mrs Lee walked to school from the library. If they walked towards each other, they would meet 4mins later. If they walked in the same direction, it would take CYTHNIA 20 mins to catch up with Mrs Lee whose walking speed was 40m/min . How far was the library from the school ? Assume that Mrs Lee's walking speed was constant at all times.

Hi

As in any Speed questions, start with a simple diagram.

In 20 minutes, Mrs Lee covered 20*40 or 800 m

In 4 minutes, Mrs Lee covered 4*40 or 160 m

In 16 minutes, CYTHNIA covered 960 m (800+160)

In 4 minutes, CYTHNIA covered 240 m (960/4)

Distance between library and school ------- 400 m (240+160)

Best wishes

[whitety]

anneshirleygilbert:

Hi whitety, this is the last lap of the race, ain't it? I remember you from before.


12 days require 60 people
1 day would require 60 x 12 = 720 people
20 days would require 720 divided by 20 = 36 people.

All the best to you and your child.

Anne

Hi Anne,

I remember you too! Thanks for your help! My mind's not working today.

All the best to your child too!

[tianzhu]

Shimmer:

Q1. Meiling and Raja started on a 36km cycling trip at the same time. They cycled at the same speed of the first 12km. For the remaining 24km , Meiling cycled at a fast speed. She arrived at the finishing point 10 mins before Raja who was 4km behind her. Raja did not change his speed throughout the trip and he completed the trip at 1110.
A) at what time did the trip start ?
B) what was Meiling'a average speed for the remaining 24 km of the trip in m/min ?

Hi

Consider Raja

10 minutes ------- 4 km

60 minutes ------- 24 km

90 minutes ------- 36 km

From 1110h, count backwards a duration of 90 minutes.

1110 -------1010 -------- 0940 (start time of trip)

Meiling took 50 minutes to complete 24 km.

50 minutes ------- 24000m

1 minute -------- 480 m

Meiling'a average speed for the remaining 24 km of the trip ------- 480 m/min

Best wishes

[Bunny27]

tianzhu:

Shimmer:

Q1. Meiling and Raja started on a 36km cycling trip at the same time. They cycled at the same speed of the first 12km. For the remaining 24km , Meiling cycled at a fast speed. She arrived at the finishing point 10 mins before Raja who was 4km behind her. Raja did not change his speed throughout the trip and he completed the trip at 1110.
A) at what time did the trip start ?
B) what was Meiling'a average speed for the remaining 24 km of the trip in m/min ?

Hi

Consider Raja

10 minutes ------- 4 km

60 minutes ------- 24 km

90 minutes ------- 36 km

From 1110h, count backwards a duration of 90 minutes.

1110 -------1010 -------- 0940 (start time of trip)

Meiling took 50 minutes to complete 24 km.

50 minutes ------- 24000m

1 minute -------- 480 m

Meiling'a average speed for the remaining 24 km of the trip ------- 480 m/min

Best wishes

Hi, someone pls help on this question:
1. The ratio of Jim's savings to Ken's savings increased by 60%.
What percentage of Ken's money must be decreased so that their savings are equal?
Thank you !!

[tianzhu]

Bunny27:

Hi, someone pls help on this question:
1. The ratio of Jim's savings to Ken's savings increased by 60%.
What percentage of Ken's money must be decreased so that their savings are equal?
Thank you !!

Hi

Could we know where this question is from?

The decrease in the percentage of Ken’s money varies as in accordance to the ratio of Jim’s savings to Ken’s savings in the beginning.

Best wishes

[tianzhu]

susutoo:

Hi, need help

1) Rita, Siva and Tara planned to share the cost of a present for their friend equally. When buying the present, Siva Tara were short of $26 altogethe. After rita paid for their share, the present was shared by Rita, Siva and
Tara in the ratio of 9:2:1 respectively. how mucn did the present cost?

Hi

Hope this helps.

Best wishes

http://farm8.staticflickr.com/7139/7674265994_d0a1a50748_z.jpg\">

[tianzhu]

susutoo:

2) http://i49.tinypic.com/2lsbpqr.jpg\">

Hi

You may work through using multiples of 3 and 4 with some logical reasoning.

It’s not too tedious in this particular case.

42 plain muffins ------- $56

28 chocolate muffins ------- $42

This satisfies the condition of $98

Average cost of muffin ------- 98/70 -------$1.40

Best wishes

[anneshirleygilbert]

Hello tianzhu,


Please help. I have trouble interpreting the question. As such, am unable to follow your working.

Q2. CYTHNIA walked to the library from school and at the same time, Mrs Lee walked to school from the library. If they walked towards each other, they would meet 4mins later. If they walked in the same direction, (this is after they met, having walked in opposition directions? or they walk from where they were at first?) it would take CYTHNIA 20 mins to catch up with Mrs Lee whose walking speed was 40m/min . How far was the library from the school ? Assume that Mrs Lee’s walking speed was constant at all times.



As in any Speed questions, start with a simple diagram.

In 20 minutes, Mrs Lee covered 2040 or 800 m

In 4 minutes, Mrs Lee covered 440 or 160 m

In 16 minutes, CYTHNIA covered 960 m (800+160)

In 4 minutes, CYTHNIA covered 240 m (960/4)

Distance between library and school ------- 400 m (240+160)

Please help.

[tianzhu]

anneshirleygilbert:

Hello tianzhu,


Please help. I have trouble interpreting the question. As such, am unable to follow your working.

Hi

It helps to have some sort of visual sketch.

I'll PM to you probably in the evening or tomorrow morning.

Best wishes

[MathIzzzFun]

Shimmer:

Need help on these two speed question !


Q2. CYTHNIA walked to the library from school and at the same time, Mrs Lee walked to school from the library. If they walked towards each other, they would meet 4mins later. If they walked in the same direction, it would take CYTHNIA 20 mins to catch up with Mrs Lee whose walking speed was 40m/min . How far was the library from the school ? Assume that Mrs Lee's walking speed was constant at all times.

Hi

alternate approach...

Distance between school & library --> 1 unit

In 4 min, total distance covered by both Cythnia & Mrs Lee = 1 unit
In 20 min, total distance covered by both Cythnia & Mrs Lee = 5 units
In 20 min,
distance covered by Mrs Lee = 20 x 40 = 800m
distance covered by Cythnia = 1 unit + 800 m
Total --> 1 unit + 1600m = 5 units
1 unit --> 400 m

Distance between school & library = 400m

cheers.