Q&A - PSLE Math

[Vanilla Cake]

Hi faith2u,


Q1
Uncle Seng bought some fruits. 1/3 of the fruits were apples, 1/9 of
them were mangoes and the rest were oranges. The prices of the
fruits are as shown :
Apples – 20 cents each
Mangoes – 70 cents each
Oranges – 30 cents each
Uncle Seng spent $15.60 on the apples and mangoes. How much did
he spend on the oranges?

A1
Ratio of the number of fruits bought
A : M
1/3 : 1/9
(Multiply both sides by 9)
3 : 1
Since total units for all three fruits was 9, units for orange = 5 ( from 9-3-1)

Cost of 1 'set' of apples and mangoes
= [(3 x 20) + (1 x 70)] cents
= (60 + 70) cents
= 130 cents

Number of 'sets' = 1560/130 = 12
Amount of money spent on oranges = 12 x 5 x 30 cents = 1800 cents = $18.00

Q2
Meili has a total of 20 mangoes and oranges. If she exchanges every
mango for 3 oranges, she will have 32 oranges. How many oranges
does she have?

A2
Assume that number of mangoes be M.
Number of oranges = (20-M)

1 mango can be exchanged for 3 oranges
M mangoes can be exchanged for 3M oranges

(20-M)+3M = 32
20 + 2M = 32
2M = 12
M = 6
Oranges = 20-6 = 14

Meili has 14 oranges

Q3
Tank A and tank B had 48 litres and 8 litres of water respectively at
first. Then an equal amount of water was added into each tank. As a
result, the ratio of the amount of water in tank A to that of tank B
became 3:1. How much water was added into each tank?

A3
Key note - Difference remain constant

(3-1)units = ( 48-8 ) litres
2 units = 40 litres
1 unit = 20 litres

20-8 = 12 litres
Amount of water added into each tank was 12 litres

[kiasiparent]

My predictions for this year PSLE maths.

I think it will be slightly more difficult than last years’.

1) Units and parts are required to solve certain tough questions. Or use cross multiply. Or use algebra. Or use guess and check lol and more.

2) Questions on Volume which generally requires calculator to solve as the numbers are very big and hard to divide.

3) Questions on guess and check (or suppose method) which generally requires calculator to solve as the numbers will be quite big.

4) Speed question which requires ratio to solve.

5) Difference of area between circle and another figure.

[radiantmum]

Chanced upon this thinking that I can help to solve some Maths problem to help but saw these educated predictions ... Can't help laughing. I've came across toto, weather, calamity predictions but 1st time PSLE. Brightens my day ! Sorry kiasiparent, dont meant to be rude. :oops:

[Tang]

Dharma:

bwpj2000:

1)Sum of first 2 odd numbers = 1+3 = 4

Sum of first 3 odd numbers = 1+3+5 = 9
Therefore sum of the first n odd numbers is n^2
So sum of first 210 odd numbers is 210^2= 44100

Not too sure about Q2. :?

Q1 Sum of odd nos. from 1 to 210 = (210/2) x (210/2) = 11025

To derive :
Sum of all nos. from 1 to 210 = 105 x 211 = 22155 (210 x 211)/2
Sum of all even nos. from 1 to 210 = 2(1+2+...+104+105) =2(105 x 106)/2 = 11130
So, (1+3 + ...+ 209) = 22155 - 11130 = 11025

Odd numbers --> 1 , 3 , 5 , ....... 209 (105th number)

Sum = (1 + 209) / 2 x 105 = 105 x 105 = 11025

[small]

Hi all,


Thanks for your time. My DD's answer is 5pm.
[quote]Question:

Mr Lee left Town M for Town N at a speed of 80km/h. Mr Ong also left Town M for town N one hour later at a speed of 100km/h. Mr Ong reached Town Q, which was was in the middle of Town M and N, 30 mins earlier than Mr Lee. If Mr Ong reached Town N at 10pm, waht time did Mr Lee leave Town M?
[/quote]

[tianzhu]

Hi


I think the answer is 9am.

Time taken by Mr Ong –> 12 hours
Time taken by Mr Lee –> 15 hrs

Where is this Q from?It can be considered as a higher order speed Q where proportion method may be more appropriate.

Best Wishes

[Vanilla Cake]

small:

Hi all,

Thanks for your time. My DD's answer is 5pm.[quote]Question:
Mr Lee left Town M for Town N at a speed of 80km/h. Mr Ong also left Town M for town N one hour later at a speed of 100km/h. Mr Ong reached Town Q, which was was in the middle of Town M and N, 30 mins earlier than Mr Lee. If Mr Ong reached Town N at 10pm, what time did Mr Lee leave Town M?

[/quote]Hi small,
Is this qn from your DD's P6 Prelim exam? The answer is 9 am.

Difference in distance between Mr Lee and Mr Ong = 1.5 x 80 = 120 km.
Required time for Mr Ong to catch up with Mr Lee = 120 / (100-80) = 6 h
Distance from Town M to Town Q = 6 x 100 = 600 km
Total distance between Town M and Town N = 600 x 2 = 1200 km
Time taken for Mr Ong to travel from Town M to Town N=1200/100 = 12 h

Since Mr Lee started 1 hour earlier, that meant he took 13 h to travel.
Use timeline:

9 am.............12 pm...................10 pm
......................3 h......................10 h

[small]

tianzhu:

Hi


I think the answer is 9am.

Time taken by Mr Ong --> 12 hours
Time taken by Mr Lee --> 15 hrs

Where is this Q from?It can be considered as a higher order speed Q where proportion method may be more appropriate.

Best Wishes

Hi Tianzhu, :celebrate:

Can you show me the working? Thanks in advance.


I am still trying to figure out Vanilla's working.... :oops:

[heutistmeintag]

Hi all, need urgent help on these 3 questions. TIA!


http://www.postimage.org/image.php?v=aVpF3Nr

http://www.postimage.org/image.php?v=aVpFqeJ

http://www.postimage.org/image.php?v=Pq1p_BgA

[small]

small:

Hi Tianzhu, :celebrate:


Can you show me the working? Thanks in advance.


I am still trying to figure out Vanilla's working.... :oops:

Hi Tianzhu and Vanilla Cake, I managed to figure out the working, thanks for oyur help. :celebrate: