Q&A - PSLE Math

[tianzhu]

its888me:

At first Alvin had twice as many trading cards as Steven. After Alvin had given away 285 of his trading cards, Steven had twice as many trading cards as Alvin. How many trading cards did they have altogether at first?
Answer is 845 but my child said it should be 570.

Hi

Your child's answer is correct.

At first

Alvin:Steven ------ 2:1 ------ 4:2

Only Alvin had given away 285 cards. Steven’s number of cards stays the same before and after.

Hence, make the number of units for Steven the same.

In the end

Alvin:Steven ------ 1:2

3 units ------- 285

1 unit ------ 95

Number of cards they had at first ------- 6*95 -------- 570

Best wishes

[Michaelia0816]

Fine but thx

[Michaelia0816]

You’ re welcome

[Michaelia0816]

I found a slide that explains my answer, it is from 1800- teacher....


http://farm4.static.flickr.com/3090/2825831587_859f719b11_o.jpg

[anneshirleygilbert]

Thank you, tianzhu. Appreciate your help very much.


Sincerely,
Anne

[jarenchuatw]

Help needed again for speed question:


May cycled from Town X to Town Y at an average speed of 6km/hr and reached Town Y at 4pm. If she cycled 2km/hr faster, shw would reach there at 3pm. At what average speed must she cycle in order to reach Town Y at 2pm?

[dicoyote]

Hi,


Need help, what method can be use for this question? guess and check?

A logistics company charges $15 for every 2 vases delivered on time and $10 for every 3 vases delivered late.
In June, the company had to deliver 500 vases.
The company collected $3675 for the delivery.
How many vases were delivered late?

[MathIzzzFun]

dicoyote:

Hi,


Need help, what method can be use for this question? guess and check?

A logistics company charges $15 for every 2 vases delivered on time and $10 for every 3 vases delivered late.
In June, the company had to deliver 500 vases.
The company collected $3675 for the delivery.
How many vases were delivered late?

Hi

one way is to \"convert\" the question to a typical \"chicken & cow\" question.
3 vases delivered late --> $10 -- 30 units (3 units/$1), 1 vase delivered late --> 10 units
2 vases delivered on time --> $ 15 --- 45 units, 1 vase delivered on time --> 22.5 units

$3675 --> 11025 units
22.5 units - 10 units = 12.5 units

Number of vases delivered late = (500 x 22.5 - 11025) ÷ 12.5 = 18

cheers.

[Michaelia0816]

MathIzzFun, I needed help, pls wait for my question, dun go offline

[MathIzzzFun]

jarenchuatw:

Help needed again for speed question:


May cycled from Town X to Town Y at an average speed of 6km/hr and reached Town Y at 4pm. If she cycled 2km/hr faster, shw would reach there at 3pm. At what average speed must she cycle in order to reach Town Y at 2pm?

Hi

use speed ratio / time ratio..

original speed : new speed --> 6 km/h : 8 km/h = 3 : 4
time taken to travel from X to Y at original speed : new speed = 4u : 3u
1u --> 1h
Distance X to Y = 6 km/h x 4h = 24 km
In order to reach Y at 2pm (ie 2h faster),
she needs to cycle at 24 / 2 = 12km/h


cheers.