Q&A - PSLE Math

[Publica]

tianzhu:

smileplease:

Please help with these 3 Qs:


1) John takes part in a race in which he needs to walk, run and cycle. He walks for 1km, runs for the next 2km and cycles for the last 3km of the race. He cycles thrice as fast as he runs and runs thrice as fast as he walks. The total time he takes to complete the 3 activities is 42 minutes more than if he has cycled for the whole journey. How much more time does he take to walk than run?

Hi

Sorry I am rushing out the solutions because you may need them urgently as your exam is near. Please bear with me if there are errors.

Q1

Time taken for
Walk ----- 9 units
Run ----- 3 units
Cycle ------- 1 unit

9 units + 6 units + 3 units -------- 6 units +42
12 units -----42
1 unit ------3.5

Walk ------ 31.5 mins
Run ------ 10.5 mins

Difference ------21 mins

Best wishes

Hi Tianzhu,

My son was working on this question and has 10.5 mins as answer. He thinks that the Run should be 21 mins instead, which is 3.5 x 6 units.

Thanks.

[tianzhu]

Daddy:

Hi tianzhu,


How you get ------2 units (25% left) for below question? Thanks.

from 25% --> fraction is 1/4.. :?


An egg seller had chicken eggs, duck eggs and quail eggs. He had 225 more quail eggs than duck eggs. After he had sold 60% of the chicken eggs, 2/3 of the duck eggs and 3 times as many quail eggs as duck eggs sold, he found that he had 25% of his quail eggs and a total of 205 eggs left. Find the total number of eggs he had first.

Thanks.

Hi

You're correct.

25% ------ 25/100 ------ 1/4 ------ 2/8

Best wishes

[tianzhu]

Publica:

Hi Tianzhu,

My son was working on this question and has 10.5 mins as answer. He thinks that the Run should be 21 mins instead, which is 3.5 x 6 units.

Thanks.

Hi

Your boy is correct.

The answer is 10.5.

I'll revise the answer.Thank you for highlighting the error.

Best wishes

[yingxuan0806]

Tanks P and Q are each filled with some water. If water from Tank Q is poured into Tank P until the water in Tank P reaches the brim, there will be 5 litres of water left in Tank Q. If water from Tank P is poured into Tank Q until the water in Tank Q reaches the brim, there will be 17 litres of water left in Tank P. The ratio of volume of Tank P to the volume of Tank Q is 3 : 1. How many more litres of water are needed to fill both tanks to their brim?

can help me solve this question? if yes, can you please use ration n algebra?? preferably dont use model method. ty in advance

[MathIzzzFun]

yingxuan0806:

Tanks P and Q are each filled with some water. If water from Tank Q is poured into Tank P until the water in Tank P reaches the brim, there will be 5 litres of water left in Tank Q. If water from Tank P is poured into Tank Q until the water in Tank Q reaches the brim, there will be 17 litres of water left in Tank P. The ratio of volume of Tank P to the volume of Tank Q is 3 : 1. How many more litres of water are needed to fill both tanks to their brim?

can help me solve this question? if yes, can you please use ration n algebra?? preferably dont use model method. ty in advance

Hi

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cheers

[gnagna]

tianzhu:

gnagna:

Hi Tianzhu
Can explain how you get 38?

Hi

Good Morning.

This question appears friendishly easy at first glance.

But, it’s not so easy for PSLE kids.

Equal circles can be stacked in square or hexagonal packing such that each circle touches four or six others.

If you use square packing, you’ll get 36 circular shapes. With hexagonal packing, you’ll get 2 more circular shapes.

Best wishes

Thanks Tianzhu for pointing out.

[tianzhu]

gnagna:

Thanks Tianzhu for pointing out.

Hi

Good Morning.

You're welcome.

Best wishes

[Vanilla Cake]

Hi tianzhu,


Good morning,
2011 MGS P6 Prelim Maths is http://mwtuition.com.sg/free-resources online but without answers. I would like DD2 to work out these sums after her PSLE 2011 LC by tomorrow afternoon. Is it possible for you to go through her answers and advise if there are any mistakes? BTW, it seems that Q12 and Q14 from paper 2 cannot be solved due to incomplete information. Pls kindly look into them as well as the above request to seek help from you.

Best wishes
VC's mum

[pensiveowl]

Hi.. could someone pls help me with this question:


Cindy had four times as many postcards as Annie. After Cindy gave 20% of her postcards to Jane and Annie gave 10% of her postcards to Jane, the number of Jane's postcards increased by 75%. Jane had 252 postcards in the end. How many postcards did Cindy have at first?

Thanks,
PO

[Vanilla Cake]

Cheerfuldad:

Hi vlim,

Do u have the solution for paper 2 - Q5, Q12, Q15b, Q16,Q17b ?I tried to solve but could not, can you help!

Hi Cheerfuldad,
While waiting for vlim's response, pls refer to the suggested solutions as below:

Q5
Total area
A : B
100 : 120
5 : 6

Assume the common shaded area to be p
Unshaded area of A = 0.8u
Unshaded area of B = u

Solve by simultaneous equations,
0.8u + p = 5
u + p = 6

0.2u = 1
u = 5
p = 1

Percentage of rectangle B that is shaded = p/p+ux100%
= 1/(1+5)x100%
= 1/6 x 100% = 16 and 2/3%

Q12
Before
A : O
4u : 5u

Change (sold)
A : O
-170 : -1.25u (25/100x5u)

After
A : O
1 : 2

2(4u-170)=1(5u-1.25u)
8u-340=3.75u
4.25u = 340
u = 80

Number of apples left = 4u-170 = 4(80)-170 = 320-170 = 150
Number of oranges left = 5u-1.25u = 3.75u = 3.75x80 = 300
Number of fruits that Mr Tan had in the end = 150+300 = 450

Q15(b)
From part (a), you worked out that after 10 min, height of water level in tank A = 15 cm @ 8.10 am
Given that flow rate of water by Tap P = 1.2 litres/min (1200 cm3/min) and Tap B = 5 litres/min (5000 cm3/min). Calculate the base area for tank A and tank B = 40x20 and 50x40= 800 cm2 and 2000 cm2. From here, work out the increase in height for both tanks.
Increase in height per min for Tank A = 1200/800 = 1.5 cm/min
Increase in height per min for Tank B = 5000/2000 = 2.5 cm/min
At 8.10 am, height of Tank B = 0 and assume the time taken for both heights of the water level in both tanks to be equal as t.
1.5t+15=2.5t+0
t=15 min
Add 15 min to 8.10 am., will give 8.25 am.

(b) At 8.25 am, height of the water level in both tanks are equal.

Q16
Pls refer to solutions by http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=69&t=280&start=4210 on page 422.

Q17(b)
Pls refer to http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=69&t=280&start=4220 on page 423.

VC's mum