Q&A - PSLE Math

[tianzhu]

YumYum:

Hi, I need help with this Qn:


Elissa needs to reach her office at a certain time.

If she drives at 90 KM/h, she will be 38 minutes early.

If she drives at 65 KM/h, she will be 18 minutes early.

If Elissa drives at 117 KM/h, how long will she take to reach her office?

Thanks

Hi

There are a few approaches to tackle this question.

One possible way is to use inverse ratios.

The faster the speed, the less time is taken.

Speed ratio ------- 90:65 -------- 18:13
Time ratio -------- 13:18

Difference -------- 20 minutes (38-18)

5 units ------- 20

1 unit ------- 4

If she drives at 90 KM/h, she takes 13*4 or 52 minutes.

Hence distance ------- 90*(52/60) ------- 78 km

Time taken to reach office@117km/h ------ 78/117 ------ 26/39 h --------- 40 minutes

Best wishes

[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?

[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.

[jewelbox]

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

[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\">