Q&A - PSLE Math

[Muffins]

Hi small,


Let me try to solve both of your earlier problems.

Q1a) 1/3 X 2/5 = 2/15 which is $10 cash cards sold (sets).
1/3 - 2/15 = 1/5 (3/15) which is amount of $15 cards sold (sets).

($10X2) + ($15X3) = $65

$3900 divided by $65 = 60 (amount of sets)

60 X 3 =180

Q1b) 2/3 = 10/15

60X10 = 600.

http://img9.imageshack.us/img9/8171/scan1n.jpg\">

Q2) 40/2 = 20

40 X 20 X 1/2 = 400

1/2 X 3.14 X 20 X 20 = 628

628 - 400 = 228

628 X 2 = 1256

1256 - 228 = 1028

1/4 X 3.14 X 40 X 40 = 1256

1256 - 1028 = 228

228 + 228 = 456

Hope I'm right!

[Tang]

Muffins:

Hi small,


Let me try to solve both of your earlier problems.

Q1a) 1/3 X 2/5 = 2/15 which is $10 cash cards sold (sets).
1/3 - 2/15 = 1/5 (3/15) which is amount of $15 cards sold (sets).

($10X2) + ($15X3) = $65

$3900 divided by $65 = 60 (amount of sets)

60 X 3 =180

Q1b) 2/3 = 10/15

60X10 = 600.

http://img9.imageshack.us/img9/8171/scan1n.jpg\">

Q2) 40/2 = 20

40 X 20 X 1/2 = 400

1/2 X 3.14 X 20 X 20 = 628

628 - 400 = 228

628 X 2 = 1256

1256 - 228 = 1028

1/4 X 3.14 X 40 X 40 = 1256

1256 - 1028 = 228

228 + 228 = 456

Hope I'm right!

Area of Quadrant - Area of Triangle

1/4 x 3.14 x 40 x 40 = 1256

1/2 x 40 x 40 = 800

1256 - 800 = 456 cm2

The total shaded area os 456 cm2.

[Muffins]

Tang,


You really know the tricks to solve problems fast, and efficiently! WOW! :shock: Are you a school teacher, by any chance?

[ChiefKiasu]

Muffins:

Tang,


You really know the tricks to solve problems fast, and efficiently! WOW! :shock: Are you a school teacher, by any chance?

Tang is a lower Secondary boy. And an extraordinary one at that. :udaman:

[youngmum]

My boy got this problem. Can someone help me to solve this?


Monkey King had 2000 pears. He gave all the pears to some monkeys. On the first day, the monkeys ate half of the total number of pears. On the second day, they ate 1/3 of the remaining pears. On the third day, they ate 1/4 of the rest of the pears. They went on to eat the pears as 1/5,1/6,1/7,…,1/2000 of the remainder of every previous day’s pears. Find the number of pears left at the end.

Thanks. By the way, please explain clearly because i m a not so smart mum.

[James Ang]

youngmum:

My boy got this problem. Can someone help me to solve this?


Monkey King had 2000 pears. He gave all the pears to some monkeys. On the first day, the monkeys ate half of the total number of pears. On the second day, they ate 1/3 of the remaining pears. On the third day, they ate 1/4 of the rest of the pears. They went on to eat the pears as 1/5,1/6,1/7,.....,1/2000 of the remainder of every previous day's pears. Find the number of pears left at the end.

Thanks. By the way, please explain clearly because i m a not so smart mum.

i calculated the remainder to be of this sequence,

1000, 666and2/3, 500, 400...
=> 2000/2, 2000/3, 2000/4, 2000/5....

the final remainder is 2000/2000 = 1 left.

Note: these pears must be magic pears because they can last for 2000 days (6years?) and also the monkeys can eat a fraction of one pear on some days.

[James Ang]

a school teacher asked me how to solve these two questions. Since these questions are common PSLE questions, I put them here for everyone's benefit to think about. If you want the answer, please let me know.


1. 80% of marbles are red marbles and 20% of them are blue marbles. 63 red marbles and 46 blue marbles are added. The red marbles now makes up 75% of marbles and blue marbles 25% of marbles. How many red marbles are there at first?

2. A van travelled from Town A to Town B at an average speed of 55km/h. A car started its journey from town B to A at 90 km/h at the same time the van started. The two vehicles passed each other 70 km from the middle of the whole journey. Find the distance between the two town

[tianzhu]

Hi

Hope this helps.

http://farm3.static.flickr.com/2486/3943048915_0697cd38f6_o.jpg\">

[youngmum]

James Ang:

i calculated the remainder to be of this sequence,

1000, 666and2/3, 500, 400...
=> 2000/2, 2000/3, 2000/4, 2000/5....

the final remainder is 2000/2000 = 1 left.

Sorry James, I don't quite understand. I only know up to the 1000 part. :oops:

[James Ang]

youngmum:

James Ang:

i calculated the remainder to be of this sequence,

1000, 666and2/3, 500, 400...
=> 2000/2, 2000/3, 2000/4, 2000/5....

the final remainder is 2000/2000 = 1 left.

Sorry James, I don't quite understand. I only know up to the 1000 part. :oops:

1st remainder = 1/2 x 2000= 1000
2nd remainder = (1 - 1/3)x 1000 = 2/3 x 1000 = 666 and 2/3
3rd remainder = (1-1/4)x 666 and 2/3 = 3/4 x 666 and 2/3 = 500
4th remainder = (1-1/5) x 500 = 4/5 x 500 = 400
and so on...

so pattern is presented as below;
1000, 666and2/3, 500, 400...
=> 2000/2, 2000/3, 2000/4, 2000/5...... 2000/2000

the final remainder is 2000/2000 = 1 left.