Q&A - PSLE Math

[MathIzzzFun]

jewelbox:

MathIzzzFun, thanks for helping me to solve the 2 qns on volume and markers on 30 May.

u r welcome

cheers.

[mumworks]

Hi,


Can help with these questions ? Thanks.

1. In 2004, 40% of the enrolment in a art class were girls. The rest were boys. 30% of the girls left the class in 2005. If there were 216 boys in the class in 2005, how many girls were in the class in 2004 ?

2. The cost of 2 kg of beef is 120% more than the cost of 1 kg of venison. 1 kg of mutton costs 20% more than the cost of 1 kg of beef. If 1 kg of mutton cost $8.64,
find the total cost of 4kg of venison and 3 kg of beef.

3. 20% of a class of 150 ballerinas were male. If some more male ballerinas joined the class, the % of male ballerinas increased to 60%. Later, 25% of the female ballerinas left the class. Find the total no. of ballerinas left in the class.

[G Tan]

cimman:

G Tan:

Can help in this sum<


Farid had $270 and Gopal had $192. Gopal spent twice as much as Farid. If Farid had twice as much money as Gopal after spending, much did Farid spend?

if you're open to using algebra and simultaneous equations, here's an approach:

http://i47.tinypic.com/2r5vjw1.png\">

with this table, and using simultaneous equations, you'll be able to solve all Transfer type problems. There will be extensions to the table, ie. more columns or more rows of (before, transfer, after) to cater for different scenarios, but basically, the logic and processing remains the same. It does not use heuristics, so it will not confuse the child on which heuristc to use.

Your answer is not the same as the answer in the book

[tianzhu]

G Tan:

Can help in this sum<


Farid had $270 and Gopal had $192. Gopal spent twice as much as Farid. If Farid had twice as much money as Gopal after spending, much did Farid spend?

Hi

You may solve it pictorially or use letters of the alphabet.

Hope this helps.

Best wishes

http://farm8.staticflickr.com/7215/7176242769_1fbd0a7bbb_z.jpg\">

[tianzhu]

mumworks:

Hi,


Can help with these questions ? Thanks.

1. In 2004, 40% of the enrolment in a art class were girls. The rest were boys. 30% of the girls left the class in 2005. If there were 216 boys in the class in 2005, how many girls were in the class in 2004 ?

Hi

2005
30% of 40% ------ 12%
Girls:Boys ------- 28%:72%

72% ------- 216
4% ------- 12
28% ------- 84

2004
70% ------- 84
100% ------ 120 (number of girls in 2004)

Best wishes

[tianzhu]

mumworks:

Hi,


2. The cost of 2 kg of beef is 120% more than the cost of 1 kg of venison. 1 kg of mutton costs 20% more than the cost of 1 kg of beef. If 1 kg of mutton cost $8.64,
find the total cost of 4kg of venison and 3 kg of beef.

Hi

Hope this helps.

Best wishes

http://farm8.staticflickr.com/7227/7178181991_bbddb600ff_z.jpg\">

[tianzhu]

mumworks:

Hi,

3. 20% of a class of 150 ballerinas were male. If some more male ballerinas joined the class, the % of male ballerinas increased to 60%. Later, 25% of the female ballerinas left the class. Find the total no. of ballerinas left in the class.

Hi

At first
Male:Female ------ 20%:80% ------- 30:120

In the end
Male:Female ------ 60%:40% ------- 180:120

Later, 25% of the female ballerinas left the class.

75% of 180 ------ 135 (female ballerinas left)

Total number of ballerinas left in the class ------ 135+120 ------- 255

Best wishes

[cimman]

G Tan:

cimman:

[quote=\"G Tan\"]Can help in this sum<


Farid had $270 and Gopal had $192. Gopal spent twice as much as Farid. If Farid had twice as much money as Gopal after spending, much did Farid spend?

if you're open to using algebra and simultaneous equations, here's an approach:

http://i47.tinypic.com/2r5vjw1.png\">

with this table, and using simultaneous equations, you'll be able to solve all Transfer type problems. There will be extensions to the table, ie. more columns or more rows of (before, transfer, after) to cater for different scenarios, but basically, the logic and processing remains the same. It does not use heuristics, so it will not confuse the child on which heuristc to use.

Your answer is not the same as the answer in the book[/quote]ah yes, careless mistake. Should solve for u instead of p.

The equations remain the same:
270 – u = 2p ------------ 1
192 – 2u = p ----------- 2
384 – 4u = 2p
270 – u = 384 – 4u
3u = 114
u = 38

[G Tan]

cimman:

G Tan:

Can help in this sum<


Farid had $270 and Gopal had $192. Gopal spent twice as much as Farid. If Farid had twice as much money as Gopal after spending, much did Farid spend?

if you're open to using algebra and simultaneous equations, here's an approach:

http://i47.tinypic.com/2r5vjw1.png\">

with this table, and using simultaneous equations, you'll be able to solve all Transfer type problems. There will be extensions to the table, ie. more columns or more rows of (before, transfer, after) to cater for different scenarios, but basically, the logic and processing remains the same. It does not use heuristics, so it will not confuse the child on which heuristc to use.

Is there any way to do withoust using algerbra??? my DD ususlly got a hard time understanding algebra method...

[cimman]

G Tan:

cimman:

[quote=\"G Tan\"]Can help in this sum<


Farid had $270 and Gopal had $192. Gopal spent twice as much as Farid. If Farid had twice as much money as Gopal after spending, much did Farid spend?

if you're open to using algebra and simultaneous equations, here's an approach:

http://i47.tinypic.com/2r5vjw1.png\">

with this table, and using simultaneous equations, you'll be able to solve all Transfer type problems. There will be extensions to the table, ie. more columns or more rows of (before, transfer, after) to cater for different scenarios, but basically, the logic and processing remains the same. It does not use heuristics, so it will not confuse the child on which heuristc to use.

Is there any way to do withoust using algerbra??? my DD ususlly got a hard time understanding algebra method...[/quote]Tianzhu has provided the solution using modelling. You can have a look at that.
In P6, algebra is part of the syllabus. If you DD finds it hard to understand algebra, it would be good to use this holiday period to start her on the subject. The school will just spend 1 month or less teaching algebra in P6 and it will be quite stressful then.

While aglebra is not an easy topic, students can manage it if given the time (ie. 6 months) and the right environment (ie. no stress). Just teach slowly and let her assimilate it. The benefits are there. She will have one more tool in her bag of tricks. For your problem, it still manageable in modelling. There are some problems with a lot of transfers and that becomes quite tedious using modelling and sometimes there are a lot of boxes to split. So the algebra method can help out there.

Ultimately, you'll have to cross the algebra bridge when you come to P6. Best to start early to give your child more time to adjust to abstract concepts.