Q&A - PSLE Math

[mum2010]

Hi,


That’s the exactly the question given to my boy.
I use guess and check, but it’s very time comsuming so wonder anyone has better method to solve those questions.

Thanks for helping…

[tianzhu]

mum2010:

Mary put some fifty-dollar notes and some ten-dollar notes into a piggy bank. There were a total of 60 notes. The total value of the fifyt-dollar notes and ten-dollar notes was equal. How much money did she put into the piggy bank?

Hi

Please ignore this post, I've mistakenly used $5 instead of $50.

Best wishes

[tianzhu]

mum2010:

On tree-planning day, 40 people planted some trees. Each man planted 3 trees and each woman planted 2 trees. The men planted 35 more trees than the woman. How many men and women were there?

Hi

You may use a heuristics known as “Make a Supposition” or \"Assumption Method\".

Please refer to one of my earlier posts in this thread as an example.

Thu Dec 30, 2010 6:58 am @page 225
http://www.kiasuparents.com/kiasu/forum/viewtopic.php?t=280&postdays=0&postorder=asc&start=2240

You'll have 23 men and 17 women.

Best wishes

[tianzhu]

mum2010:

Benny has 24 notes which totals to $168. They are in two-dollar, five-doller adn ten-dollar denominations. How many of each kind of notes does he have?

Hi

It's not too tedious to use GC in this questions.The last digit is 8, which means we'll have multiples of $2 notes as the limiting factor.

4 number of $2
8 number of $5
12 number of $10.

Another possible answer.

9 number of $2
0 number of $5
15 number of $10.

Best wishes

[iFruit]

mum2010:

Please help!


Benny has 24 notes which totals to $168. They are in two-dollar, five-doller adn ten-dollar denominations. How many of each kind of notes does he have?

10x + 5y +2z = 168

Now, z can only be 4 or 9 or 14 and so on, as 10x +5x can only be a multiple of 10.

z can't be 9 ( or higher), because then the remaining notes will be 15 and all of them will have to be $10 notes. So z = 4.

Then

10x + 5y = 160
x +y = 20 ---> 5x + 5y = 100

From the 2 equations we get, x = 12, y= 8

so $10 = 12; $5 = 8, $2 = 4;

HTH

[Florence88]

If anybody can help to solve some of the problem sums listed below.


1) A's pocket money is 20% more than B, but 20% less than C. If their total pocket money is $2,220, find the amount each individual has ?

2) Tap A takes 5 mins to fill 1/4 of a container while tap B takes 10 min. If both the taps are turned on at the same time, how long does it take to fill up the container ?

3) The ratio of boys to girls was 3:2. After 2 boys and 3 girls joined in, the ratio became 4:3. How many girls were there at first ?


Thanks for the help :?

[Andrew Lee]

Hi...

http://postimage.org/image/n5mxfo1w/
:?

[iFruit]

Florence88:

If anybody can help to solve some of the problem sums listed below.


1) A's pocket money is 20% more than B, but 20% less than C. If their total pocket money is $2,220, find the amount each individual has ?

Assume B's pocket money = 100u

A's pocket money = 120u

C's pocket money = 100/80 x 120u = 150u

A+B+C = 100u + 120u +150u = 370u = 2220-----> u =6

A = 120u = 720
B = 100u = 600
C = 150u = 900

[iFruit]

Florence88:

If anybody can help to solve some of the problem sums listed below.


2) Tap A takes 5 mins to fill 1/4 of a container while tap B takes 10 min. If both the taps are turned on at the same time, how long does it take to fill up the container ?

Tap A takes 5 mins to fill 1/4 of a container --->Tap A takes 1 mins to fill 1/20 of a container

Tap B takes 10 mins to fill 1/4 of a container --->Tap B takes 1 mins to fill 1/40 of a container

In 1 min, Tap A & B fill = 1/20 + 1/40 = 3/40 of the container

Time taken to fill the container = 40/3 = 13 1/3 mins

[iFruit]

Florence88:

3) The ratio of boys to girls was 3:2. After 2 boys and 3 girls joined in, the ratio became 4:3. How many girls were there at first ?


Thanks for the help :?

Let girls = 2u
Boys = 3u

3u +2: 2u+3 = 4:3

3(3u+2) = 4(2u+3)---> 9u +6 = 8u +12---->u=6

girls at first = 2u = 12

HTH.