Q&A - PSLE Math

[tianzhu]

dicoyote:

Have a similar question to q3 from kiasuaunt....here goes


A car left Town X for Town Y at the same time when a motorcycle left Town Y for Town X. The average speed for the car is 88 km/h wile the average speed of the motorcycle was 64km/h. The two vehicles passed each other at a point 33 km from the midpoint between Town X and Town Y. What was the distance between Town X and Town Y?

Thanks

Hi

There are a few approaches to tackle this question.

In 1h, the car and motorcycle covered a combined distance of (88+64) or 152km.

Hence, the mid point is at 152/2 ------ 76 km

In 1h, the distance from the midpoint is 12 km (88-76) or (76-64)

33/12 ------- 2.75

The car and motorcycle travelled for 2.75h

Therefore, the distance between Town X and Y -------- 2.75*152 ------ 418km

Best wishes

[mom-of-2 0]

Thank you Tianzhu !


Sometimes I wonder how 12 year olds are supposed to figure this out

[kiasuaunt]

MathIzzzFun:

kiasuaunt:

Hi.


Q1.
Mr Lee sold 15% of his cupcakes on Monday.
He sold 90 fewer cupcakes on Tuesday than on Monday.
He then sold 70 fewer cupcakes on Wednesday than on Tuesday.
On Thursday,he sold 330 cupcakes and found that he had half of his original number of cupcakes left.
How many cupcakes did he sell altogether?

Q2.
There are some red and green beans in a container.
If Ahmad removes 20 red beans, the ratio of the number of red beans to the number of green beans becomes 6:5.
If Ahmad removes 10 green beans, the ratio of the number of red beans to the number of green beans becomes 4:3.
How many beans are there in the container?

Q3.
Town Lala and Town Yaya are 840 km apart.
At 8.30 am, a car left Town Lala for Town Yaya , travelling at a constant speed.
At the same time, a lorry set off from Town Yaya for Town Lala at a constant speed too. At 1.30 pm, the 2 vehicles passed each other. If the speed of the car was 24 km/h faster than the lorry, find the speed of the car.

Thank you.

Hi
Q3.
8.30am to 1.30pm --> 5h
5h x 24 km/h --> 120 km
when the car and the lorry passed each other, the car travelled 120 km more than the lorry.

Total distance --> 840 km, car travelled 120 km more than the lorry -- can you continue from here ? ie sum of two numbers = 840, difference of the numbers = 120.

cheers.

Hi - I understand Q2.

For Q1: Tues - left 70u+90. Why +90?

For Q3: (840-120)/2 = 360 km ( distance of the lorry when the vehicles meet)

Speed of car = (360+120)/5 = 96 km/hr

Is the ans. correct?

Thank you.

[tianzhu]

kiasuaunt:

Hi

For Q3: (840-120)/2 = 360 km ( distance of the lorry when the vehicles meet)

Speed of car = (360+120)/5 = 96 km/hr

Is the ans. correct?

Thank you.

Hi

Your answer is correct.

Another possible approach

Speed of lorry ------- 360/5 ------- 72

Speed of car -------- 72 + 24 ------- 96

Best wishes

[AJH]

:thankyou: Tianzhu for your clear explanations.

[tianzhu]

kiasuaunt:

Hi.

Q1.
Mr Lee sold 15% of his cupcakes on Monday.
He sold 90 fewer cupcakes on Tuesday than on Monday.
He then sold 70 fewer cupcakes on Wednesday than on Tuesday.
On Thursday,he sold 330 cupcakes and found that he had half of his original number of cupcakes left.
How many cupcakes did he sell altogether?

Hi

A neat way is to use MD.

Hope this helps.

Best wishes

http://farm8.staticflickr.com/7220/7353643500_a0f577ed8d_z.jpg\">

[tianzhu]

AJH:

:thankyou: Tianzhu for your clear explanations.

Hi

You're welcome.

Best wishes

[tianzhu]

mom-of-2:

Thank you Tianzhu !


Sometimes I wonder how 12 year olds are supposed to figure this out

Hi

You're welcome.

To begin with, I must say this is not an easy question for PSLE kids.

Best wishes

[YumYum]

Hi, I need help with this Qn:


Elissa needs to reach her office at a certain time.

If she drives at 90 KM/h, she will be 38 minutes early.

If she drives at 65 KM/h, she will be 18 minutes early.

If Elissa drives at 117 KM/h, how long will she take to reach her office?

Thanks

[tianzhu]

YumYum:

Hi, I need help with this Qn:


Elissa needs to reach her office at a certain time.

If she drives at 90 KM/h, she will be 38 minutes early.

If she drives at 65 KM/h, she will be 18 minutes early.

If Elissa drives at 117 KM/h, how long will she take to reach her office?

Thanks

Hi

There are a few approaches to tackle this question.

One possible way is to use inverse ratios.

The faster the speed, the less time is taken.

Speed ratio ------- 90:65 -------- 18:13
Time ratio -------- 13:18

Difference -------- 20 minutes (38-18)

5 units ------- 20

1 unit ------- 4

If she drives at 90 KM/h, she takes 13*4 or 52 minutes.

Hence distance ------- 90*(52/60) ------- 78 km

Time taken to reach office@117km/h ------ 78/117 ------ 26/39 h --------- 40 minutes

Best wishes