Q&A - PSLE Math

[tianzhu]

Essential:

Good Day Tianzhu, please help as not sure how to solve this question . 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 ?

Hi

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

[peggy]

Please assist.


There two bags of jelly beans labelled A and B. In bag A, there 470 red jelly beans and 480 green jelly beans. In Bag B, there are 350 jelly beans and 200 green jelly beans. Some red and green jelly beans from bag B are transferred to bag A. As a result, 60% of the jelly in bag A and 20% of those in bag B are red. How many red and green jelly beans are transferred from bag B to bag A ?

Thanks!

[kwcllf]

Tank A, base measuring 60cmx10cm and height 40cm is empty. Tank B, base measuring 50cmx20cm and height 36cm, is 1/3 filled with water. Water is poured into the two tanks at the same time at a rate of 1.2 litres per minute.


How long it take for the height of the water to be the same in both tanks?

Thanks!

[Winx5015]

Thanks MathIzzzfun.

[Winx5015]

Hi, can anyone help to solve this question.


In a hall, 3/5 of the pupils were girls. After some of the boys left the hall, the ratio of the number of girls to the number of boys increased to 5:2.
(a) If there were 36 boys left, how many pupils were there at first?
(b) At the beginning, the ratio of the number of girls who were in red T-shirts to those in black T-shirts was 4:5. 20% of the girls were in blue T-shirts. The number of girls in black T-shirts was the same as the number of boys in black T-shirts. If 20% of the remaining boys were in red T-shirts, how many boys were in blue T-shirts?

Thanks!

[tianzhu]

peggy:

Please assist.


There two bags of jelly beans labelled A and B. In bag A, there 470 red jelly beans and 480 green jelly beans. In Bag B, there are 350 jelly beans and 200 green jelly beans. Some red and green jelly beans from bag B are transferred to bag A. As a result, 60% of the jelly in bag A and 20% of those in bag B are red. How many red and green jelly beans are transferred from bag B to bag A ?

Thanks!

Hi

This question looks familiar.

It touches on SE.

You may use MD, UP or use letters of the alphabet to show the variables.

Due to time constraints, I’ll just provide some pointers using UP.

At first

Bag A

R:G ------ 470:480

Bag B

R:G ------ 350:200

After the transfer

Bag A

R:G ------ 3u:2u

Bag B

R:G ------ 1p:4p

3u + 1p ------- 820 (470 + 350)

2u + 4p ------ 680 (480 + 200)

5u + 5p ------ 1500

1u + 1p ------300

2u + 300 ------ 820

2u ----- 520

1u ------ 260

Bag A

R:G ------ 3u:2u ------- 780:520

Red ----- 780 – 470 ------ 310

Green ----- 520 - 480 ------ 40

Best wishes

[tianzhu]

Winx5015:

Hi, can anyone help to solve this question.


In a hall, 3/5 of the pupils were girls. After some of the boys left the hall, the ratio of the number of girls to the number of boys increased to 5:2.
(a) If there were 36 boys left, how many pupils were there at first?
(b) At the beginning, the ratio of the number of girls who were in red T-shirts to those in black T-shirts was 4:5. 20% of the girls were in blue T-shirts. The number of girls in black T-shirts was the same as the number of boys in black T-shirts. If 20% of the remaining boys were in red T-shirts, how many boys were in blue T-shirts?

Thanks!

Hi

You may use MD or UM.

Before

B:G ----- 2:3 -------- 10:15

After

B:G ----- 2:5 ------ 6:15

The number of girls remains the same before and after. Make the number of units showing girls the same.

6 units ------ 36

1 unit ------ 6

Number of pupils @ first -------- 25*6 ------- 150

Number of girls@first ------ 15*6 ------- 90

Number of girls in blue T-shirts ------- 18 (20% of 90)

90 – 18 ------ 72

Girls in red T shirt: Girls in black T shirt ------- 4:5 -------- 32:40

The number of girls in black T-shirts was the same as the number of boys in black T-shirts.

Number of boys in black T shirt ------- 40

Number of boys@first ----- 60

60 – 40 ------- 20

Number of boys in red T shirt ------ 20% of 20 -------- 4

Number of boys in blue T shirt ------- 20 – 4 ------- 16

Best wishes

[tianzhu]

kwcllf:

Tank A, base measuring 60cmx10cm and height 40cm is empty. Tank B, base measuring 50cmx20cm and height 36cm, is 1/3 filled with water. Water is poured into the two tanks at the same time at a rate of 1.2 litres per minute.


How long it take for the height of the water to be the same in both tanks?

Thanks!

Hi

1 litres ------- 1000 cubic cm

1.2 litres/min ------ 1200 cubic cm/min

Tank A

Base area ------- 600 sqcm

In 1 min, the increase in height ------- 1200/600 ------- 2 cm

Tank B

Base area ------- 1000 sq cm

In 1 min, the increase in height ------- 1200/1000 ------- 1.2 cm

Height of water in tank B ------- 12 cm (1/3 filled)

Difference in height -------- 2 – 1.2 ------- 0.8

Time taken for height of the water to be the same in both tanks ------- 12/0.8 -------- 15 minutes

Best wishes

[kwcllf]

Thank you, Tianzhu :thankyou:

[peggy]

Tianzhu,


Thanks for your answer. Much appreciated.

Have a great weekend !