Q&A - PSLE Math

[portal]

3)I have this question to ask as well.An empty retangular tank 0.5 meters long and 0.4 meters wide is filled with water from 2 taps,Tap A and Tap B.Tap A

was turned on and it fills the tank with water at a rate of 9 litres per minute.Tap B was turned on and it fills the tank with water at a rate of 11 litres per minute.What is the height of the water in the tank after Tap B was turned on for 10 minutes? leave your answer in meters. :imdrowning:

[YumYum]

Dear Tianzhu,


Thank you.

I have another Qn:

The average mass of a group of girls is 38 kg. If one more pupil with a mass of 50 kg joins the group, the average mass will become 40 kg. Find the number of girls in the group first.

Thanks

[tianzhu]

portal:

1)I have this question to ask.A faulty weighing scale showed a reading of 0.3kg when nothing was placed on it. A box which contained 18 identical magazines was placed on the weighing scale, After 2/9 of the magazines were removed from the box, the weighing scale showed a reading of 7.82kg. The mass of each magazine was 60% the mass of the box. What is the mass of the box? Give your answer in grams. :?:

Hi

Number of magazines ------14(7/9*18)

7.82 - 0.3 ------- 7.52

1 magazine ------3 units
1 box ------ 5 units

(14*3) + 5 ------47

47 units ------ 7520
1 unit ------ 160

Mass of box ------5*160 ------800g

Best wishes

[tianzhu]

portal:

2)I have another question to ask.


3/4 of the fruits are apples and the rest are oranges.5/6 of the apples and 210 oranges were sold.The number of fruits left is 1/5 of the total.How many fruits were sold? :?:

Hi

For Q2, you may use UM or MD.

I’ll give you some pointers.

Use 40 units.

Apples sold -------- 25 units (5/6 of 30 units)
Apples left ------- 5 units

1/5 of fruits left ------- 1/5*40 -------8 units

Oranges left ------- 8-5 ------ 3 units

Oranges sold ------ 10-3 ------ 7 units

Oranges sold ------- 210

7 units ------ 210
1 unit ------- 30

32*30 ------- 960(number of fruits sold)

Best wishes

[tianzhu]

YumYum:

Dear Tianzhu,


Thank you.

I have another Qn:

The average mass of a group of girls is 38 kg. If one more pupil with a mass of 50 kg joins the group, the average mass will become 40 kg. Find the number of girls in the group first.

Thanks

Hi

You're welcome.

50 - 40 ------10

40 - 38 ----- 2

10/2 -----5 (number of girls at first)

Best wishes

[peggy]

Hi,


Please help me with this qtn.

On Wednesday, the ratio of the number of chicken wings sold to the number of curry puffs sold was 5:4. The amt of money collected was $73.60. On Thursday, the ratio became 1:3 and $8.80 less was collected. If the ratio of the price of chicken wing to the price of a curry puff is 3:2, find the ratio of the number of chicken wings sold on Wednesday to Thursday.

Thank you.

[small]

portal:

3)I have this question to ask as well.An empty retangular tank 0.5 meters long and 0.4 meters wide is filled with water from 2 taps,Tap A and Tap B.Tap A

was turned on and it fills the tank with water at a rate of 9 litres per minute.Tap B was turned on and it fills the tank with water at a rate of 11 litres per minute.What is the height of the water in the tank after Tap B was turned on for 10 minutes? leave your answer in meters. :imdrowning:

Hi,

Let me try to solve.

Base of the rectangular tank ----- 0.5m x 0.4m = 0.2 m square

I presumed Tap A and Tap B were turned on together
Every 1 minute ----- 11 + 9 = 20 litres
after 10 minutes ----- 20 x 10 = 200 litres = 0.2 m cube (1000 litres =1 m cube)

Height of tank x 0.2 m square =0.2 m cube
Height of tank = 1 m

[small]

peggy:

Hi,


Please help me with this qtn.

On Wednesday, the ratio of the number of chicken wings sold to the number of curry puffs sold was 5:4. The amt of money collected was $73.60. On Thursday, the ratio became 1:3 and $8.80 less was collected. If the ratio of the price of chicken wing to the price of a curry puff is 3:2, find the ratio of the number of chicken wings sold on Wednesday to Thursday.

Thank you.

Hi,

Saw this question in somewhere.


Wed-------------------- Wing : Puff
Sold ratio ------------- 5u : 4u
price ratio ------------- 3 : 2
Money collected ------15u : 8u (total value= S73.60)
In proportion----------- $48.00 : $25.60


Thurs ------------------- Wing : Puff
Sold ratio --------------- 1p : 3p
price ratio --------------- 3 : 2
Money collected ------- 3p : 6p (total value is $73.60 - $8.80 = $64.80)
In proportion-------------- $21.60 : $43.20


Ratio of Wings sold on Wed to Thurs ---------- 48 : 21.6
Ratio of Wings sold on Wed to Thurs ---------- 4 : 1.8 -----> 40 : 18 -----> 20 : 9

[peggy]

Hi Small,


Thanks for your solution.

Have a Great Day !!! :rahrah:

[mathfreak]

YumYum:

Dear Tianzhu,


Thank you.

I have another Qn:

The average mass of a group of girls is 38 kg. If one more pupil with a mass of 50 kg joins the group, the average mass will become 40 kg. Find the number of girls in the group first.

Thanks

Solution:
When the pupil with mass of 50 kg joins the group, imagine that the \"extra mass\" of the pupil, which is just 50 - 40 = 10 kg, is distributed among the other pupils of mass 38 kg. This means that the 10 kg is distributed among 10 ÷ (40 - 38) pupils, or 5 pupils. Hence, there were 5 girls in the group at first.
Just to be sure, we check: (38x5+50)÷6 is indeed 40.