Q&A - PSLE Math

[tianzhu]

Winx5015:

:thankyou: tianzhu

Hi

You're welcome.

Best wishes

[tianzhu]

Michaelia0816:

Pls help me with the following question, Tianzhu! 1) A rectangular tank, 1/3 filled with water, has a square base of 4m2. The ratio of its height to its length is 3:5. A tap is turned on and water flows into the tank at a constant rate of 2m3 per minutes. How long will it take to fill the take completely with water.

2) A cuboid has a square face of area 64 cm2. The ratio of its breadth to its length is 2:5. When the cuboid is placed into the tank, 40 cm by 25 cm by 20 cm, the water level reaches the 12 cm mark. Calculate, in litres, the volume of water in the tank? Pls write down the method! :?:

Hi

Q1)Square base ------- 4 sqm

Length (breadth) ----- 2m

height: length ------- 3:5 ------- 1.2:2

The tank is 1/3 filled with water.

Additional volume of water required -------4*0.8 ------ 3.2 cubic m

2 cubic m ------ 1 min

3.2 cubic m ------ 1.6 min

For Q2, please check with your school teacher if volume of solid in displacement of volume is in the syllabus.

Breadth of cuboid ------- 8

Breadth:length ------- 2:5 ------- 8:20

Volume of cuboid ------- 64*20 ------- 1280 cubic cm

Volume of water + cuboid in tank ------- 40*25*12 ------- 12000 cubic cm

Volume of water in tank ------- 12000 – 1280 ----- 10720 cubic cm ------ 10.72 l

Best wishes

[Michaelia0816]

Thank you for your help, Tianzhu! :thankyou:

[thinkgmama]

Hi,

Kindly help with this qn from my daughter’s worksheet.

1) The number of stamps that Mary and Henry had at first was in the ratio 3:1. After Mary bought 56 stamps and Henry sold 15 stamps, Mary then had 6 times as many stamps as Henry. How many stamps did Henry have at first?

2) Ali and Ben shared a sum of money in the ratio of 1:4. If Ali gives Ben $36, Ben will have 6 times as much money as Ali. How much money does Ben have?

[Bunny27]

thinkgmama:

Hi,

Kindly help with this qn from my daughter's worksheet.

1) The number of stamps that Mary and Henry had at first was in the ratio 3:1. After Mary bought 56 stamps and Henry sold 15 stamps, Mary then had 6 times as many stamps as Henry. How many stamps did Henry have at first?

2) Ali and Ben shared a sum of money in the ratio of 1:4. If Ali gives Ben $36, Ben will have 6 times as much money as Ali. How much money does Ben have?

Hi, pls help on this question :

Janice's monthly income is $300 more than Betty's but their monthly expenditures are the same. Over a period of time, Janice saved $1700 while Betty only saved $500.

a) How long does each of them take to save the given amount of money?

b) Given that each of them $1500 per month, what is Janice's monthly income?

Thanks ...

[tianzhu]

Bunny27:

Hi, pls help on this question :

Janice's monthly income is $300 more than Betty's but their monthly expenditures are the same. Over a period of time, Janice saved $1700 while Betty only saved $500.

a) How long does each of them take to save the given amount of money?

b) Given that each of them $1500 per month, what is Janice's monthly income?

Thanks ...

Hi

Good morning.

Janice saved $1700 while Betty only saved $500.

1700 – 500 ------ 1200

Janice's monthly income is $300 more than Betty's

1200/300 ------- 4

They took 4 months.

b)

I think there is some missing word in the highlighted phrase.

Given that each of them spends $1500 per month.

1700/4 ------ 425

Janice’s monthly salary ------ 1500 + 425 ----- 1925

Best wishes

[tianzhu]

thinkgmama:

Hi,

Kindly help with this qn from my daughter's worksheet.

1) The number of stamps that Mary and Henry had at first was in the ratio 3:1. After Mary bought 56 stamps and Henry sold 15 stamps, Mary then had 6 times as many stamps as Henry. How many stamps did Henry have at first?

2) Ali and Ben shared a sum of money in the ratio of 1:4. If Ali gives Ben $36, Ben will have 6 times as much money as Ali. How much money does Ben have?

Hi

Good Morning.

For Q2, you may use MD or UM.

At first
Ali:Ben - ------ 1:4 (5) ------- 7:28 (35)

Change
Ali:Ben ------- -36:+36

In the end
Ali:Ben - ------ 1 :6 (7) ------- 5:30 (35)

The amount of money remains the same before and after.
Make the total number of units the same.

2 units ------ 36
1 unit ------ 18

Ben ------ 28*18 ------ 504

For Q1, please check your question.

I’ve found a similar question to yours, some numbers are different.

If the question is revised as shown, then you may use “Units and Parts’ to solve it.

The number of stamps that Mary and Henry had at first was in the ratio 3 : 1. After Mary bought 36 stamps and Henry sold 20 stamps, Mary then had 5 times as many stamps as Henry. How many stamps did Henry have at first?

At first
Mary’s stamps : Henry’s stamps ----- 3 units:1 unit

Change
Mary’s stamps : Henry’s stamps ----- +36: -20

In the end
Mary’s stamps : Henry’s stamps ----- 5 parts:1 part

3 units + 36 ------ 5 parts

1 unit – 20 ------ 1 part
(x5)
5 units – 100 ------ 5 parts

Equalise the parts or cross multiply.

3 units + 36 ------ 5 units – 100
2 units ------ 136
1 unit ------ 68

Henry ------ 68 stamps (at first)

Now, try to do your question, change 56 to 66.

Best wishes

[2DMommy]

Please help me with these two questions :


1) Sally has a bottle containing some red and blue beads. If she adds another 10 red beads, 60% of the beads in the bottle are blue. If she adds another 30 blue beads, 75% of the beads in the bottle are blue. How many red beads are in the bottle ?

2)Susan has some vanilla and chocolate sweets in her bag. If she adds 20 vanilla sweets into the bag, the percentage of vanilla sweets in the bag becomes 40%. If she adds 30 chocolate sweets in the bag, there will be 70% of chocolate sweets in the bag. How many vanilla and chocolate sweets does she have ?

Thank you !

[tianzhu]

2DMommy:

2)Susan has some vanilla and chocolate sweets in her bag. If she adds 20 vanilla sweets into the bag, the percentage of vanilla sweets in the bag becomes 40%. If she adds 30 chocolate sweets in the bag, there will be 70% of chocolate sweets in the bag. How many vanilla and chocolate sweets does she have ?

Thank you !

Hi

Q2 has been discussed earlier.

Best wishes

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[tianzhu]

2DMommy:

Please help me with these two questions :


1) Sally has a bottle containing some red and blue beads. If she adds another 10 red beads, 60% of the beads in the bottle are blue. If she adds another 30 blue beads, 75% of the beads in the bottle are blue. How many red beads are in the bottle ?
Thank you !

Hi

Where is your Q1 from?

Sometimes, the introduction of the word “another” in the conditions can be opened to interpretation.

This question has been floating around regularly in forums.

I have some red and blue ribbons in a bottle.
If I add 20 red ribbons, 60% of my ribbons are blue.
If I add another 60 blue ribbons, 75% of my ribbons are blue.
How many ribbons do I have in the bottle?

Depending on one’s interpretation of the word another in the second condition, one may end up with 180 or 80.

It’ll be helpful if current PSLE students or their parents help to clarify with their school teachers on this question.

For your Q1, I’m more inclined to go for

First scenario
Red beads ------ 2 units – 10
Blue beads ------ 3 units

Second scenario
Red beads ------ 2 units - 10 -------- 1 part
Blue beads ------ 3 units + 30 ------- 3 parts

6 units – 30 -------- 3 units + 30

3 units ------- 60
1 unit ------ 20

Number of red beads -------- 30

Best wishes