Q&A - PSLE Math

[tianzhu]

2632parent:

Need help in the following question on speed,


1) Ali and Ben started jogging from Park X to Park Y at the same time. Ali jogged at an average speed of 7.5 km/h while Ben jogged at an average speed of 4.5km/h. After jogging for 1.2h, Ali decided to turn back and jog toward Ben. Ali met Ben at Point Z which was halfway between Park X and Park Y. Ali and Ben then continued their jog together toward Park Y at an average speed of 4.5km/h. What was the distance between Park X and Park Y.

Thank you

Hi

Good Morning.

As usual for Speed questions, start with a simple diagram.

X at one end, W at the midpoint and Y at the other end.

After jogging 1.2h

Ali ------- 1.2*7.5 ------- 9km

Ben ------- 1.2*4.5 ------- 5.4km

Hence, to the right of W, draw a point A to show the position of Ali.

Also, draw a point B before W to represent the position of Ben.

Distance between Ali and Ben ------- 3.6 km (9-5.4)

In 1h, Ali and Ben covered 12 km (7.5 + 4.5)

Hence, they would covered 3.6 km in 0.3h (3/10)

Distance covered by Ben in 0.3h -------- 4.5*0.3 ------- 1.35

Distance from X to W ------- 1.35 + 5.4 -------- 6.75

Distance between Park X and Park Y ---------- 6.75*2 -------- 13.5km

Alternatively, if students are familiar with inverse proportion, they may also use it to calculate the distance travelled by Ben.

Speed ratio

Ali:Ben ------- 7.5:4.5 -------- 5:3

The distance ratio remains the same as 5:3

Distance covered by Ben --------3/8*3.6 -------- 1.35 km

Best wishes

[2632parent]

Thank you councillor for your early morning reply. Really appreciate your solution, thank you.

[small]

Hi,


Please help and many thanks in advance.

http://i49.tinypic.com/331lstd.jpg\">

[its888me]

tianzhu,


Thanks for helping me in solving the 2 Questions. Really appreciate it!

[Essential]

Need help, please kindly assist. At 11am a car left town P for Town Q. Travelling at a speed of 80 km/h. At the same time , another car left town Q for town P at a speed of 100 km / h . The distance between the two towns was 720 km.at what time did the cars pass each other ?

[its888me]

So sorry, another question from Nanyang prelim 2010 again, Q11:


Diagram A shows a closed rectangular tank of dimensions 20cm by 20cm by 40cm with a cube of edge 10cm glued to its bottom left corner. The tank contains 12 litres of water.

Diagram B shows the same rectangular tank lying on its side. Find the height of the water level, in cm, corrected to 2 decimal places.

http://i48.tinypic.com/302o09z.jpg\">

Again, TIA!

[its888me]

one last question 18. Thank you!


http://i48.tinypic.com/34zkcxj.jpg\">

[tianzhu]

its888me:

one last question 18. Thank you!


http://i48.tinypic.com/34zkcxj.jpg\">

Hi

This question has been discussed before.

Q18 looks intimidating at first glance. It helps if one can rearrange the shaded areas.

What I am sharing here may help students who prefer to work with more familiar shapes. It may not be the shortest way.

Interestingly, the rearranged figure looks like a big eye and a small eye.

PSLE students should be familiar with calculating the areas of shaded area within the 3cm square (big eye) and the small eye within the 1cm square.

The area of the shaded area in Q18 is the 2(area of big eye – area of small eye)

Best wishes

http://farm5.staticflickr.com/4085/4988720284_36afd045ba_z.jpg\">

[cimman]

small:

Hi,


Please help and many thanks in advance.

http://i49.tinypic.com/331lstd.jpg\">

http://i48.tinypic.com/24o5c85.png\"> http://i47.tinypic.com/14lls41.png\">

as you can see from the above tessellations, there are quite a few options for the larger shape. I've highlighted one of the options in red outline for each tessellation.

[pandu]

Emily earns a commission on 12% for the first 5 encyclopaedias she sells. For any additional sales, she will get a 15% commission.

Each encyclopaedia is sold at $140. If she receives a total commission of $462, how many encyclopaedias does she sell altogether?