Q&A - PSLE Math

[speedmaths.012624com]

kiasuaunt:

Car A left Singapore for Penang. Car B left Penang for Singapore at the same time using the same route. 3 hrs after the two cars had set off, they were 760 km apart. 5 hrs after they had set off, the distance between the two cars was 400 km. How many hrs after setting off would the two cars meet?


Thanks.

Hi,

The cars took 5 - 3 = 2 hours to close up 760 - 400 = 360 km.
The cars took 2 hours to close up 360 km.
The cars will take another 400/360 x 2 = 2 2/9 hours to close up the last 400 km.

5 + 2 2/9 = 7 2/9 hours.

Hope this helps.

Cheers


speedmaths.com

[jewelbox]

Hi, how do i do these 2 qns. Thks.

1. A shopkeeper had some markers in red and blue. If 50 red markers and 25 blue markers were sold each week, there would be 500 red markers left when all the blue markers were sold. If 25 red markers and 50 blue markers were sold each week, there would be 800 red markers left when all the blue markers were sold. How many markers did the shopkeeper have at first? Ans:1100

2. Tank A measures 30cm by 20cm by 24 cm. It contains 12600 cubic cm of water. Tank B has a square base of length 25cm and is filled with water upto a ht of 11.2cm. The water in Tank A is then poured into B until the water levels in both tanks are the same.
a) What is the water level in Tank B at the end? Ans: 12
b) Water is then poured from B back into A such that the water level in A is 1.5 times the water level in B. What is the water level in A? Ans:19.28

[MathIzzzFun]

jewelbox:

Hi, how do i do these 2 qns. Thks.

1. A shopkeeper had some markers in red and blue. If 50 red markers and 25 blue markers were sold each week, there would be 500 red markers left when all the blue markers were sold. If 25 red markers and 50 blue markers were sold each week, there would be 800 red markers left when all the blue markers were sold. How many markers did the shopkeeper have at first? Ans:1100

Hi

number of red & blue markers are the same in both cases.
in both cases, all blue markers were sold.
case 2,
red markers sold : blue markers sold --> 25 : 50 = 1u : 2u
case 1,
red markers sold : blue markers sold --> 50 : 25 = 4u : 2u (same number of blue markers were sold)

Total red markers remain the same,
1u + 800 (case 2) = 4u + 500 (case 1)
1u --> 100

Total number of markers --> 6 x 100 + 500 (or 3 x100 + 800, case 2) = 1100

cheers.

[MathIzzzFun]

jewelbox:

Hi, how do i do these 2 qns. Thks.

1. A shopkeeper had some markers in red and blue. If 50 red markers and 25 blue markers were sold each week, there would be 500 red markers left when all the blue markers were sold. If 25 red markers and 50 blue markers were sold each week, there would be 800 red markers left when all the blue markers were sold. How many markers did the shopkeeper have at first? Ans:1100

2. Tank A measures 30cm by 20cm by 24 cm. It contains 12600 cubic cm of water. Tank B has a square base of length 25cm and is filled with water upto a ht of 11.2cm. The water in Tank A is then poured into B until the water levels in both tanks are the same.
a) What is the water level in Tank B at the end? Ans: 12
b) Water is then poured from B back into A such that the water level in A is 1.5 times the water level in B. What is the water level in A? Ans:19.28

Hi

answer key for a is not correct.
a)
total volume of water in A & B = 12600 + 25 x 25 x 11.2 = 19600 cubic cm
total base area = 30 x 20 + 25 x 25 = 1225 square cm
height in both tanks when water level is the same
= 19600/1225 = 16cm

b)
height of water level in tank A --> 3u
height of water level in tank B --> 2u
total volume of water = 3u x 30x20 + 2ux 625 = 19600
1u --> 392/61 cm
height of water level in tank A = 3 x 392/61 = 19.28 cm (to 2 decimal places)

cheers.

[whitety]

Hi, Need help on 2 qns:


Q1. Mrs Devi and Mrs Singh made a total of 675 pies. After selling some pies each, the number of pies Mrs Devi had left was 4 times the number of pies she sold and the number of pies Mrs Singh had left was thrice the number of pies she sold. Given that both of them had a total of 531 pies left, how many pies did Mrs Devi have at first ?

Q2. 2/3 of the number of Jacob’s trading cards was equal to 1/4 the number of Samy’s trading cards. After each of them bought 52 trading cards, Samy ended up with twice as many trading cards as Jacob. How many trading cards did Samy have at first ?

Thanks!

[MathIzzzFun]

whitety:

Hi, Need help on 2 qns:


Q1. Mrs Devi and Mrs Singh made a total of 675 pies. After selling some pies each, the number of pies Mrs Devi had left was 4 times the number of pies she sold and the number of pies Mrs Singh had left was thrice the number of pies she sold. Given that both of them had a total of 531 pies left, how many pies did Mrs Devi have at first ?


Thanks!

Hi

Q1..

http://i49.tinypic.com/nbamc1.png\">

cheers.

[MathIzzzFun]

whitety:

Hi, Need help on 2 qns:



Q2. 2/3 of the number of Jacob's trading cards was equal to 1/4 the number of Samy's trading cards. After each of them bought 52 trading cards, Samy ended up with twice as many trading cards as Jacob. How many trading cards did Samy have at first ?

Thanks!

Hi

2/3 Jacob = 1/4 Samy
2/3 Jacob = 2/8 Samy

Jacob's cards --> 3 units } difference = 5 units
Samy's cards --> 8 units }

Each bought 52 tradings cards --> difference remain the same.
after the purchase
Jacob's cards --> 5 units
Samy's cards --> 10 units

2 units --> 52
1 unit --> 26

Samy's cards at first --> 8 x 26 = 208

cheers.

[whitety]

Hi MathIzzzFun,


Thank you very much for your help!

[Spongy]

Hi, pls help. Thank you!


1. In 320, 3>2>0, that is, the digits in the hundreds place, tens place and ones place are in decreasing order. How many such 3-digit numbers are there?

2. Mark has a bag of sweets. He repacks 3/4 of them into small packets of 15 sweets each and the rest into large packets of 25 sweets each. Find the ratio of the number of large packets to the number of small packets.

[tianzhu]

Spongy:

Hi, pls help. Thank you!

1. In 320, 3>2>0, that is, the digits in the hundreds place, tens place and ones place are in decreasing order. How many such 3-digit numbers are there?

Hi

First thing first, is such a question within the PSLE syllabus?

Where is your question from?

Most probably, PSLE students would think of \"Systematic Listing\" as this a a strategy covered in the syllabus.However, it's tedious.

Please check with your school teacher if it is within the syallabus.

The answer is 120.

Best wishes