Q&A - PSLE Math

[YumYum]

tianzhu:

YumYum:

Hi, can someone pls help with these Qns:


1) on the first day of a camp, there were 240 more boys than girls. On the second day, 20% of the boys left the camp and the number of girls increased by 10%. in the end, there were 42 more girls than boys. How many children were there at the camp on the first day?
Thanks!

Tianzhu, thks for the explanation.


Hi

First day
Boys ---- 10 units + 240
Girls ---- 10 units

Second day
Boys ---- 8 units + 192
Girls ---- 11 units

11 units ------ 8 units + 192 + 42
1 unit ------ 78

Number of children@first day ------- 20units + 240 ------- 1800

Best wishes

[the shadowed snake]

Hi I need help on this Q by today please ANS it as soon as possible


George and Hamid drove at constant speed from City A to City B.They started their journey at the same time. When George completed 3/4 of the journey,Hamid was 18km behind George . George reached City B 20 min before Hamid. Find Hamid's speed in km/h.
:?: :?: :?: :?: :?: :?:
MANY thanks in advanced :thankyou: :thankyou: :thankyou: :thankyou: :thankyou: :thankyou: :thankyou: :thankyou: :thankyou: :thankyou:

[Mary Joy]

please help me with these speed questions


1.Mr Tan travelled from town A to town b.he took 2.5 hours to travel the first 156 km and 3/5 of that time to travel the remaining 2/5 of the journey.what was his average speed for the whole journey?

2.susan drove from city mall to parklane mall at an average speed of 80 km/h.Danny left city mall one hour earlier than Susan and took 5 hours to reach parklane mall,traveling at an average speed of 72 km/ h.danny reached parklane mall at 8 pm.
a) at what time did Susan leave city mall?
b) how far was Susan from parklane mall when Danny reached the destination?

:thankyou: :lovesite:

[tianzhu]

the shadowed snake:

Hi I need help on this Q by today please ANS it as soon as possible


George and Hamid drove at constant speed from City A to City B.They started their journey at the same time. When George completed 3/4 of the journey,Hamid was 18km behind George . George reached City B 20 min before Hamid. Find Hamid's speed in km/h.

Hi

As in any speed question, start with a simple diagram.

When George completed 3/4 of the journey, Hamid was 18km behind George.

Hence, When George completed the whole journey, Hamid was 24km behind George.

Hamid took 20 minutes to complete 24 km.

20 minutes ------ 1/3 h

Hamid's speed ------- 24/1/3 ------ 72km/h

Best wishes

[the shadowed snake]

tianzhu:

the shadowed snake:

Hi I need help on this Q by today please ANS it as soon as possible


George and Hamid drove at constant speed from City A to City B.They started their journey at the same time. When George completed 3/4 of the journey,Hamid was 18km behind George . George reached City B 20 min before Hamid. Find Hamid's speed in km/h.

Hence, When George completed the whole journey, Hamid was 24km behind George.

WHY??????? :? :? :? :? :? :? is it like this????

[tianzhu]

fullhope:

Hi everyone, can anyone help:

Every Saturday, John will go for his usual exercise. if he runs up 32 steps and walks up 68 steps , he will take 184 seconds. If he runs up 50 steps and walks 50 steps, he will take 175 seconds. If he runs at the same rate throughout the whole exercise, how long will he take to run the 100 steps?
Thank you!

Hi

It helps to start with a simple diagram.

Run 18 steps instead of walk 18 steps saves 9 seconds (184-175)

2 steps ------ 1 second

50 steps ------- 25 seconds

175 – 25 ------- 150

He’ll take 150 seconds to run 100 steps.

Best wishes

[tianzhu]

the shadowed snake:

WHY??????? :? :? :? :? :? :? is it like this????

Hi

As given in the question, when George completed 3/4 of the journey, Hamid was 18km behind George.

So when George completed 1 /4 or 1 part of the journey, Hamid was 6 km behind George, when George completed 1/2 or 2 parts of the journey, Hamid was 12 km behind George.

Therefore, when George completed the whole journey, Hamid was 24 km behind George.

Best wishes

[PapayaDad]

tianzhu:

the shadowed snake:

WHY??????? :? :? :? :? :? :? is it like this????

Hi

As given in the question, when George completed 3/4 of the journey, Hamid was 18km behind George.

So when George completed 1 /4 or 1 part of the journey, Hamid was 6 km behind George, when George completed 1/2 or 2 parts of the journey, Hamid was 12 km behind George.

Therefore, when George completed the whole journey, Hamid was 24 km behind George.

Best wishes

and so hamid took 20 minutes to cover 24km
his speed is 24 x 3 = 72km/h
(change 20 minute to 1 hour by 20 x 3 = 60 minutes ; so distance also multiply 3)

[mathnoobs]

MathIzzzFun:

http://i40.tinypic.com/ztj18k.png\">

looks like both are cyclists and Bala is certainly a pro-racer.

cheers.

Hi MathIzzzFun
I’m afraid I don’t quite understand how to simplify the following expression:
(18 units – 60km)/9units x 18
In your example, this will simplify to 36 units – 120 km
I’m stuck at how to eliminate the 9units from the denominator.

thanks

[tianzhu]

Mary Joy:

please help me with these speed questions


1.Mr Tan travelled from town A to town b.he took 2.5 hours to travel the first 156 km and 3/5 of that time to travel the remaining 2/5 of the journey.what was his average speed for the whole journey?

Hi

Good Morning.

It’s helpful to start with a simple diagram.

Draw a line with 3 parts equal to 156 km. Hence, 1 part ------ 52km.

Mr Tan took 2.5h to cover 156 km.

3/5 of 2.5 h ------ 1.5 h

remaining 2/5 of the journey -------- 2*52 ------- 114 km

Total distance -------- 260 (156+114)

Total time ------- 4 (2.5+1.5)

Average speed -------- 260/4 ------ 65 km/h

Best wishes