Q&A - PSLE Math

[zsqchx]

tianzhu:

zsqchx:

Please help me to solve Q 16 of Henry park 2011


Mr Lee took 7 hours to tavel from town A to Town B while Mr Wong took 8 hours to travel from Town B to Town A. Both of them did not change their speed throughout the journey. Both of them started off at the same time and moved towards each other. 3 hours later, they were 110 km apart. what was the speed Mr Lee was driving?

Thanks

Hi

Good Morning.

As in any question on “Speed”, it’s helpful to draw a simple diagram showing the relationships between two motorists.

Use a common multiple of 56 (7 and

Mr Lee
1h ------ 8 units

Mr Wong
1h ------7 units

In 1h they travelled 15 units
In 3h, they travelled 45 units.

56 – 45 ------11
11units ------ 110

1 unit ------ 10
8 units ------80

Mr Lee ------- 80km/h

Best wishes

Hi Tianzhu,

Thank you for your help

[tianzhu]

htn:

tianzhu

thanks.

Hi

You're welcome.

Best wishes

[tianzhu]

P.KH:

Dear tianzhu , thanks a lot for your quick reply .. It was really helpful . 

Hi

You're welcome.

Best wishes

[tianzhu]

zsqchx:

Hi Tianzhu,

Thank you for your help

Hi

You're welcome.

Best wishes

[kavisuresh]

Pls help in solving these questions from 2009 prelims.

1. A rectangular tank with dimesnions 130cm by 100cm by 210cm was 30% filled with water. 8 identical pails of water, completely filled , were scooped out of it from it and this resulted in a drop of the water level to 38cm. The remaining amt of water was transferred into a cubical tank containing 39l of water. The water was then drained out through a tap at the bottom of the cubical tank at 13l per minute. a) what is the capacity of each pail ? b) How long did it take to drain water from cubical tank completely ?

2.A car and a coach travelled from town A to town B. The coach left Town A at 0648 and it took 5h to reach town B. The car started 30minutes later than the coach and it took 4hours to reach town B. At what time did the car catch up with the coach ?

3. Aaron and kumar took part in a 24km marathon. Aaron ran half the distance at a speed of 10km/h and jogged the rest of the way at a speed of 8km/h. Kumar ran half of his total time at 12km/h and jogged the rest of the time at 6km/h. If they started the marathon at 8am, at what time would each of them finish ?

4. 65% of the animals on a farm were cows and the rest were goats. When 240 more cows and goats were added to the farm the percentage of cows increased by 20% and the number of goats doubled. How many goats were there on the farm at first ?

5. There are some black and white marbles in a bag. If 20black marbles are removed from the bag, the total number of marbles left will be 7times the number of black marbles left. If 50 white marbles are removed from the bag, the total number of marbles left will be 5times the number of black marbles left. How many marbles are there in the bag ?

Thanks you.

[tianzhu]

kavisuresh:

2.A car and a coach travelled from town A to town B. The coach left Town A at 0648 and it took 5h to reach town B. The car started 30minutes later than the coach and it took 4hours to reach town B. At what time did the car catch up with the coach ?

Hi

This question was discussed in an earlier post.

Please follow this link.
http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=69&t=280&hilit=0648+5h&start=1500

Best wishes

[tianzhu]

kavisuresh:

4. 65% of the animals on a farm were cows and the rest were goats. When 240 more cows and goats were added to the farm the percentage of cows increased by 20% and the number of goats doubled. How many goats were there on the farm at first ?

Hi

At first
Cow ----- 65 units
Goat -----35 units

In the end
Cow ----- 78 units (up 20%)
Goat -----70 units (double or twice)

(13+35) -----48
48 units ------ 240
1 unit ----- 5

35 units ------5*35 ------175 (goat at first)

Best wishes

[tianzhu]

kavisuresh:

5. There are some black and white marbles in a bag. If 20black marbles are removed from the bag, the total number of marbles left will be 7times the number of black marbles left. If 50 white marbles are removed from the bag, the total number of marbles left will be 5times the number of black marbles left. How many marbles are there in the bag ?

Hi

The “if” in the statement signifies that the condition only applies to that particular scenario and not to any other ones.

Scenario 1 ------ at first
Black ------ 1 unit + 20
White ------ 6 units

Scenario 2 ------at first
Black ------- 1 part
White ------ 4 parts +50

1 part ------ 1 unit + 20
6 units ------ 4 parts + 50

6 units -------4(1 unit + 20) + 50
6 units ------4 units +80 +50

2 units ----- 130
1 unit ------ 65

Total number of marbles ------ 7 units + 20 ------- 7(65) + 20 ------ 475.

Best wishes

[tianzhu]

kavisuresh:

3. Aaron and kumar took part in a 24km marathon. Aaron ran half the distance at a speed of 10km/h and jogged the rest of the way at a speed of 8km/h. Kumar ran half of his total time at 12km/h and jogged the rest of the time at 6km/h. If they started the marathon at 8am, at what time would each of them finish ?

Hi

Aaron
12/10 ------ 1.2h
12/8 ------ 1.5h

Total time ------2.7 h -------2h 42 min

Kumar
Speed -----12:6 -------2:1
Distance ----- 2:1

3 units ------24km
1 unit ------8km

Kumar ------ 16/12 ------ 1h 20 min
8/6 ------ 1h 20min

Total time ------ 2h 40 min

Best wishes

[tianzhu]

kavisuresh:

1. A rectangular tank with dimesnions 130cm by 100cm by 210cm was 30% filled with water. 8 identical pails of water, completely filled , were scooped out of it from it and this resulted in a drop of the water level to 38cm. The remaining amt of water was transferred into a cubical tank containing 39l of water. The water was then drained out through a tap at the bottom of the cubical tank at 13l per minute. a) what is the capacity of each pail ? b) How long did it take to drain water from cubical tank completely ?

Hi

Volume of water in rectangular tank ------- 0.3(130*100*210) ------- 819000

Amount of water left ------- 130*100*38 ------- 494000

Difference in volume ------- 819000 – 494000 ------- 325000

Volume or capacity of 1 pail -------325000/8 ------ 40625

Change 494000 cubic cm to litres which is 494 litres

(494+39)/131------- 41 mins.

Best wishes