Q&A - PSLE Math

[mama_10]

MathIzzzFun:

mama_10:

Hi,


Need help in this question.
Class A and Class B have the same number of pupils. The ratio of the number of boys in Class A to the number of boys in Class B is 3:2. The ratio of the number of girls in Class A to the number of girks in Class B is 3:5. Find the ratio of the number of boys to the number of girls in Class A.

Thank you!

Since the Class A and Class B have same number of pupils, the difference between number of boys in A and B, and the difference between the number of girls in A and B, must be the same.

Boys --> Class A : Class B = 3 : 2 = 6 : 4
Girls --> Class A : Class B = 3 : 5
ratio of number of boys to number of girls in A = 6 : 3 = 2 : 1


http://i45.tinypic.com/15gc6qs.png\">

cheers.

Sorry, I dont understand why change the Boys ratio from 3:2 to 6:4?
thank you

[kwcllf]

mama_10:

MathIzzzFun:

[quote=\"mama_10\"]Hi,


Need help in this question.
Class A and Class B have the same number of pupils. The ratio of the number of boys in Class A to the number of boys in Class B is 3:2. The ratio of the number of girls in Class A to the number of girks in Class B is 3:5. Find the ratio of the number of boys to the number of girls in Class A.

Thank you!

Since the Class A and Class B have same number of pupils, the difference between number of boys in A and B, and the difference between the number of girls in A and B, must be the same.

Boys --> Class A : Class B = 3 : 2 = 6 : 4
Girls --> Class A : Class B = 3 : 5
ratio of number of boys to number of girls in A = 6 : 3 = 2 : 1


http://i45.tinypic.com/15gc6qs.png\">

cheers.

Sorry, I dont understand why change the Boys ratio from 3:2 to 6:4?
thank you[/quote]
Boys --> Class A : Class B = 3 : 2 = 6 : 4
Girls --> Class A : Class B = 3 : 5

Since the number of pupils in Class A and Class B are the same,
when you change the ratio from 3 : 2 to 6 : 4,
The ratio of the total number of Boys + Girls in Class A = 6+3 = 9

The ratio of the total number of Boys + Girls in Class B = 4+5 = 9

When they are equal, then you can compare.

[libran269]

can we use equations/algebra to solve?

Is this have to be solved using the above method?
I am familirising the methods used for maths.
Thanks

[MathIzzzFun]

mama_10:

MathIzzzFun:

Hi,


Need help in this question.
Class A and Class B have the same number of pupils. The ratio of the number of boys in Class A to the number of boys in Class B is 3:2. The ratio of the number of girls in Class A to the number of girks in Class B is 3:5. Find the ratio of the number of boys to the number of girls in Class A.

Thank you!

Since the Class A and Class B have same number of pupils, the difference between number of boys in A and B, and the difference between the number of girls in A and B, must be the same.

Boys --> Class A : Class B = 3 : 2 = 6 : 4
Girls --> Class A : Class B = 3 : 5
ratio of number of boys to number of girls in A = 6 : 3 = 2 : 1


http://i45.tinypic.com/15gc6qs.png\">

cheers.

Sorry, I dont understand why change the Boys ratio from 3:2 to 6:4?
thank you

.. hope this explains...

http://i46.tinypic.com/120schf.png\">

cheers.

[Lazy snake]

:heresmyfish: Hi,I'm new here. :rahrah:

[Easy-going]

Hi

Desperately need help in solving this sum for my son.
Putri and David each have some money. If Putri spends $20, the ratio of the amount of money Putri has to the amount of money David has will become 3:7. If David spends $20, the ratio will become 8:12. How much money does each boy have?

[Jwoofamily]

Using units and parts method.


putri : 8 parts - 20 = 3U which means 24 parts = 9U + 60
David : 7U - 20 = 12 parts which means 24 parts = 14U - 40

Therefore, 9U + 60 = 14U - 40
Answer is U = 20

That means, Putri has 3U which means $60 after spending $20. That means Putri should have $80. David has 7U which means $140.

[MathIzzzFun]

Easy-going:

Hi

Desperately need help in solving this sum for my son.
Putri and David each have some money. If Putri spends $20, the ratio of the amount of money Putri has to the amount of money David has will become 3:7. If David spends $20, the ratio will become 8:12. How much money does each boy have?

Using MD.. hope it is readable....

http://i48.tinypic.com/znue.png\">

cheers.

[Easy-going]

Thanks

[mathnoobs]

Hi all, need help on the concept of inverse proportion rates and direct proportion rates.


As I understand it, water rates problems are direct proportion rates. As the number of taps increases, the amount of water flow increases, or the amount of job done increases.

People working on a job is inverse proportion rates. Ie.
5 cleaners takes 4 hours to clean a house. How long does 10 cleaners take to clean the same house ?
The answer would be 2 hours. As the number of cleaners increase, the time it takes to clean the house decreases, so the number of resources is inversely proportional to the time it takes to get the job done.

Taking the same reasoning, the water rate problem should also be an inverse proportion rate , as the number of taps increases, the amount of time it takes to get the job done (to fill the tank)decreases.

So, if I have a problem that says: 5 taps take 4 hours to fill a tank. How long does 10 taps takes to fill the same tank ? (assume all taps have the same rate) Would this be the same logic as the Cleaner problem ?