Q&A - PSLE Math

[tianzhu]

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Please help and once again thanks.


Question:
Ah Seng walks to school at an average speed of 4km/h every day.One day,after walking a distance of 1 km,he realised that his watch was slow.So,he ran at a constant speed and managed to reach school just in time.Later,he calculated that if he had run at this speed right form the start of the journey,he would have reached school 5 minutes earlier.What was his running speed?

Hi

As in any question on Speed, it's helpful to start with a simple diagram.

Walking

4 km ----- 1h (60 mins)
1 km ----- 15 mins.

If he had run at this speed right form the start of the journey,he would have reached school 5 minutes earlier.

15 - 5 ----- 10

Running
1 km ----- 10 mins
6 km ----- 60 mins

Hence, running speed ----- 6 km/h

Best wishes

[tianzhu]

Chan09:

Need some help: nan hua SA1 2011 question 15

The ratio of rectangle A to area of rectangle B to rectangle C is 1:2:8. If 1/4 of B is shaded, what is the ratio of the area of the shaded part to the area of the unshaded part of the figure?

there is a picture which shows 3 rectangles with C > B > A though not sure how to scan this pic here?

And: 1:15

Hi

A:B:C ----- 1:2:8 ------ 2:4:16

1 units of B is shaded.
15 units are unshaded

Hence the ratio of the area of the shaded part to the area of the unshaded part of the figure is 1:15

Best wishes

[small]

Tianzhu,

Once again many thanks…

[small]

Another speed question, please help and TIA..


Question:
An oil tanker, which left Town X for Town Y, travelled at an average speed of 50 km/h. A car, which left Town X some time later, managed to overtake the oil tanker after travelling 4/9 of the distance between towns X and Y. From then, the car took 4 and 2/5 hours to reach Town Y. If the oil tanker was 30 km away when the car reached Town Y, how long did the oil tanker take to travel from Town X to Town Y?

[MathIzzzFun]

small:

Another speed question, please help and TIA..


Question:
An oil tanker, which left Town X for Town Y, travelled at an average speed of 50 km/h. A car, which left Town X some time later, managed to overtake the oil tanker after travelling 4/9 of the distance between towns X and Y. From then, the car took 4 and 2/5 hours to reach Town Y. If the oil tanker was 30 km away when the car reached Town Y, how long did the oil tanker take to travel from Town X to Town Y?

Hi
Time taken for oil tanker to travel 5/9 of the distance = 22/5 + 30/50 = 5h
Time taken for oil tanker to travel from X to Y = 9/5 x 5 = 9h

cheers.

[small]

MathIzzzFun:

small:

Another speed question, please help and TIA..


Question:
An oil tanker, which left Town X for Town Y, travelled at an average speed of 50 km/h. A car, which left Town X some time later, managed to overtake the oil tanker after travelling 4/9 of the distance between towns X and Y. From then, the car took 4 and 2/5 hours to reach Town Y. If the oil tanker was 30 km away when the car reached Town Y, how long did the oil tanker take to travel from Town X to Town Y?

Hi
Time taken for oil tanker to travel 5/9 of the distance = 22/5 + 30/50 = 5h
Time taken for oil tanker to travel from X to Y = 9/5 x 5 = 9h

cheers.

Huge thanks MathIzzzFun...

[MathIzzzFun]

small:

MathIzzzFun:

[quote=\"small\"]Another speed question, please help and TIA..


Question:
An oil tanker, which left Town X for Town Y, travelled at an average speed of 50 km/h. A car, which left Town X some time later, managed to overtake the oil tanker after travelling 4/9 of the distance between towns X and Y. From then, the car took 4 and 2/5 hours to reach Town Y. If the oil tanker was 30 km away when the car reached Town Y, how long did the oil tanker take to travel from Town X to Town Y?

Hi
Time taken for oil tanker to travel 5/9 of the distance = 22/5 + 30/50 = 5h
Time taken for oil tanker to travel from X to Y = 9/5 x 5 = 9h

cheers.

Huge thanks MathIzzzFun...[/quote]u r welcome

have a great week !

cheers.

[tianzhu]

small:

Tianzhu,

Once again many thanks..

Hi

Good Morning.

You're welcome.

Best wishes

[keinic]

Hi


Would greatly appreciate if someone could help with the following question:

Tank X contained 40L of petrol at first. Tank Y, which is empty, fills at a rate of 26.7L per minute for 4 minutes before the tap filling tank X is turned on. Tank X fills at a rate of 18.5L per minute. Petrol is leaking from the bottom of Tank Y at a rate of 1.2L per minute.

a. How much petrol is in Tank Y 1 minute after the tap in Tank X is turned on ?
b. How long will it take for Tank Y to contain 146L more petrol than Tank X?

Tks.

[small]

keinic:

Hi


Would greatly appreciate if someone could help with the following question:

Tank X contained 40L of petrol at first. Tank Y, which is empty, fills at a rate of 26.7L per minute for 4 minutes before the tap filling tank X is turned on. Tank X fills at a rate of 18.5L per minute. Petrol is leaking from the bottom of Tank Y at a rate of 1.2L per minute.

a. How much petrol is in Tank Y 1 minute after the tap in Tank X is turned on ?
b. How long will it take for Tank Y to contain 146L more petrol than Tank X?

Tks.

Hi.

HTH..

a) 1 minute after the tap in Tank X is turned on means TanK Y was filled for 5 minutes.

Tank Y ---- 5 x (26.7-1.2) = 127.5 litres

b)
Before tap on for Tank X, Tank Y was on for 4 mins:
Volume difference between Tank Y and Tank X ----- (25.5 x 4) - 40 = 62 litres

We will need to fill up the gap between Tank X and Tank Y, so when Tank Y is 146 litres more than Tank X, the gap is :

146 - 62 = 84 litres

After tap on for Tank X :
Volume difference between Tank X and Tank Y in every 1 minute ----- (25.5 - 18.5) = 7 litres

84 / 7 = 12 mins