Q&A - PSLE Math

[Zhu99]

2DMommy:

Please help me with these questions :


1) Paris had a total of 1686 red, blue, green marbles for sales. The ratio of the number of red marbles to the number of blue marbles is 2:3. After Paris sold 75% of the blue marbles and 50% of the green marbles and none of the red marbles, she had 922 marbles left. How many blue marbles were there at first ?

2) If Sam gives Terry $350, he will have 4 times as much money as Terry. If Sam gives Terry $550, he will have thrice as much money as Terry. How much money does Sam have ?

Thank you !

1)

R : B = 2 : 3 = 8 : 12 --- [to get whole number for 25% of Blue]

25/100 x 12 = 3 u

8 + 12 = 20 u

20 u + 2 p ---> 1686

8 + 3 = 11 u

11 u + 1 p --> 922
22 u + 2 p --> 2 x 922 = 1844

2 u ---> 1844 - 1686 = 158

B: 12 u ---> 158/2 x 12 = 948

There were 948 blue marbles.


2)

S [][ .550. ][][ .550. ][][ .550.][ .550.]
T [][ 550 ]

S [][350][][350][][350][][350][350]
T [][350]

4 u + 5 x 350 ---> 3 u + 4 x 550
1 u ---> 2200 - 1750 = 450

3 x 450 + 4 x 550 = 3550

Sam has $3550.

[charsen]

altp10:

tianzhu:

[quote=\"altp10\"]http://i45.tinypic.com/2vbrbdf.jpg\">


Hi. Can someone help me out with this question please?

Thank u in advance.

Hi

I don’t have time to prepare a more colourful slide.

This basic idea is to have proper zonings.

Hope this is good enough for you.

Best wishes

http://farm9.staticflickr.com/8319/7935008548_65a59e6ecf_z.jpg\">

Thanks alot tianzhu. I had managed to get E+G=228 but didn't know if it was right. Now after your zoning, I can see how you dissected the figure to get the difference between E & F. I was also trying to work my way to get F but thought how is it possible when P6 haven't even learn Trigonometry.

Cheers..[/quote]Hi
When you are encountering these type of problems,it does not necessarily have to find the two shaded parts.Tianzhu workings was more like of grouping to me.You can find shaded parts by canceling the same unshaded parts in the figure which is part of the shaded parts.For example,you can find the difference in area of the shaded parts by taking away part G from the figure .Then,you subtract area e+a - a+f.The difference between them is the answer as the extra parts a would be cancelled off automatically.
cheers.

[Chan09]

Need help on this?

4 children decide to weigh themselves 3 at a time. Only 4 different readings were repeatedly recorded:
99.5kg, 108.1kg, 111.7kg and 116.3kg.
Find the total mass of the heaviest and lightest child?
Ans: 74.6kg

[altp10]

Hi Charsen


Thank you for the pointers. Thats another good method that you have helped me to see.

Cheers…

[its888me]

Nan Hua prelim 2011, Q15.


A car left Town A at 0800 and travelled to Town B at an average speed of 60 km/h. At the same time, a lorry left Town B for Town A. At 1130, the car and the lorry were 85km apart after passing each other eralier. If the car arrived at Town B at 1300, at what time would the lorry arrive at Town A?

Answer is 1400, but seems that it’s not right.

TIA!

[dicoyote]

Hi Hi,


Need some guide on these two questions, thanks in advance

1) Andy can dig a hole in 3 hours.
Peter can dig a similar hole in 2 hours.
Roslan can dig a similar hole in 6 hours.
Fariq can dig a similar hole in 4 hours.
If they all worked together at their own speed, how long would it take to dig a hole?

2) There were 1200 peope in Room A and Room B. 30% of the 800 people in Room A were women. 40% of the people in Room B were men. After some people in both rooms had changed rooms, 25% of the people in Room A and 75% of the people in Room B were women. How many people were there in Room A after the change?

[tianzhu]

its888me:

Nan Hua prelim 2011, Q15.


A car left Town A at 0800 and travelled to Town B at an average speed of 60 km/h. At the same time, a lorry left Town B for Town A. At 1130, the car and the lorry were 85km apart after passing each other eralier. If the car arrived at Town B at 1300, at what time would the lorry arrive at Town A?

Answer is 1400, but seems that it's not right.

TIA!

Hi

This question has been discussed before.

It’s useful to have a pictorial representation for Speed questions.

I’ll just provide some pointers.

Draw a bar, and label A and B at both ends.

At 1130, the car is at point C and the lorry is at point D.(D is nearer to A).

From 0800 to 1130, the car covered 60*3.5 ----- 210 km (A to C)

From 1130 to 1300, the car covered 60*1.5 ----- 90 km (C to B)

Distance (B to D) travelled by lorry from 0800 to 1130 ------ 90 + 85 ------ 175 km

From here, lorry’s speed ------ 175/3.5 ------- 50 km/h

From point D to A, the lorry covered (210 – 85) which is 125 km

Time taken by lorry ------125/50 ------ 2.5 h

From 1130h, add 2.5h, this gives 1400 h

Best wishes

[tianzhu]

dicoyote:

1) Andy can dig a hole in 3 hours.
Peter can dig a similar hole in 2 hours.
Roslan can dig a similar hole in 6 hours.
Fariq can dig a similar hole in 4 hours.
If they all worked together at their own speed, how long would it take to dig a hole?

Hi

One possible way, use common multiple.

A common multiple of 3,2,6 and 4 is 12.

Number of units required to dig a hole ------ 12

Andy ------ 4 units (12/3)

Peter ------ 6 units

Roslan ------ 2 units

Fariq ------ 3 units

4+6+2+3 ------- 15 units (If they all worked together at their own speed)

Time taken ------- 12/15*60 ------ 48 minutes

Best wishes

[MathIzzzFun]

dicoyote:

Hi Hi,


Need some guide on these two questions, thanks in advance


2) There were 1200 peope in Room A and Room B. 30% of the 800 people in Room A were women. 40% of the people in Room B were men. After some people in both rooms had changed rooms, 25% of the people in Room A and 75% of the people in Room B were women. How many people were there in Room A after the change?

Q2.
here are some similar questions that may help:
http://www.flickr.com/photos/62167097@N02/6858744276/in/set-72157629537287046/

http://www.flickr.com/photos/62167097@N02/7080366811/in/set-72157629537287046

cheers.

[MathIzzzFun]

dicoyote:

Hi Hi,


Need some guide on these two questions, thanks in advance

1) Andy can dig a hole in 3 hours.
Peter can dig a similar hole in 2 hours.
Roslan can dig a similar hole in 6 hours.
Fariq can dig a similar hole in 4 hours.
If they all worked together at their own speed, how long would it take to dig a hole?

Q1...
In 12 hours,
Andy --> 4 holes
Peter --> 6 holes
Roslan --> 2 holes
Fariq --> 3 holes
Total :
Andy+Peter+Roslan+Fariq
--> 15 holes in 12 hours
--> 1 hole in 12/15 h or 48 min

cheers.