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5x PSLE Math questions: 2009, 2012, 2013, 2017, 2020

 
Here are the questions posted at The Straits Times.
 
 
 
 

The trick here is the blocks of Ken. It contains the extra “12” if you would want to compare with Jim ratio from sweets to chocolates. It is because the ratio of sweets at Jim and Ken are both “1”. Hence, to find the 3 units of Jim, you need to include the “12” in the 4 blocks, that gives you a unit of 22.

To find Ken’s sweets, do remember to add back the “12” as the unit of 22 mentioned above is for Jim.

a) Remember the bakery is exactly half-way between the two houses.

Hong cycled 120m more and Jeya cycled 120m less too!

In total, Hong cycled 120m x 2 = 240m more than Jeya.

b) Hong cycled 15 m/minute faster than Jeya.

240m/ 15 = 16 minutes.

You can imagine in this way. In order to cycle 240m more than Jeya, Hong needed to cycle 16 minutes because every minute, he was 15m more than Jeya.  

Hong and Jeya timings were the same, both travel time were 16 minutes. 

Jeya speed was 70meter per minute, traveled 16 minutes. That told us the distance was 1120 meter.

a) The slower machine is the one running 100 minutes (say machine B).

So, 1 pm (13: 00) minus 100 minutes gives you 11.20 am. Easy!

b) They printed the same number of copies with machine A took 70 minutes and machine B took 100 minutes. The equation is nothing but 70*A = 100*B, re-arrange the equation to find out the ratio A to B is 10:7. From here, you know machine A has 3 units more than machine B, and machine A printed 6 more copies per minute. Hence, 1 unit is 2 copies per minute.

Put back the unit value into the ratio, you get machine A 10 x 2 copies = 20 copies per minute.

Machine B 7x 2 copies = 14 copies per minute.

To find the total number of copies printed by machine A & B , (20 x 70 ) + (14 x 100 ) = 2,800 copies.

The important note here is the ratio unit is copies per minutes. The value of “6” indicate machine A printed 6 more copies per minute.

You can get it wrongly easily if you do not do it at the right sequence.

The important message here is each of the ribbon length is 110 cm.

With ribbon sold in rolls of 25m, that’s 2500 cm / 110 cm = 22.73 ~=22 pieces of ribbon.

One roll can make 22 pieces of ribbon.

 To make 200 pieces of ribbon, you need at least 200/22 = 9.09 ~=10 rolls to make 200 pieces of ribbon.

This question is tricky if you don’t pay the attention on the key words of possible numbers.

We first find the pattern of the group of 5 which contain 3 stars and 2 hearts.

Immediately, you will find out 135 stars / 3 = 45 groups.

45 groups x 2 hearts = 90 hearts. This is easy.

However, do take note the last two pattern of the group, the last 45th group, you can also cut off the last heart but still get 135 stars. So, the possible numbers of hearts on that piece of tape can be 89 hearts too besides the norm of 90 hearts. Get it?

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