Tricky 2017 PSLE Math Question

PSLE Math Question

Let’s take a look at one of the trickier questions that challenged our children in this year’s PSLE Math paper. After that, we’ll look at how we can modify the question to help reinforce concepts as well as to further challenge our children’s abilities.

Some of our student’s parents have asked us about this tricky 2017 PSLE Math question. They heard that some students answered it wrongly and they themselves were ‘tricked’ as well! How can we understand this question? Let us review the question, explain why some students fell into this ‘trap’ and provide the model answer.

As a bonus, we will go further to ask alternative questions aimed at reinforcing a child’s understanding, as well as to further challenge them.

The PSLE Math Question


Jess wants 200 ribbons of length 110 cm for a party.
However, the ribbons were sold at 25 m per tape.
How many tapes will Jess need?

 

The Common Mistake

The common mistake is to ‘connect’ all the tapes into one single ribbon – which if we think about it, does not work in real life. Once our children make this fatal mistake, their answer will look something like this:

 

The Correct Answer

Our children needs to think of how they would get whole 110 cm lengths of ribbon. Thus they should be figuring out how ribbons of 110 cm in length could be cut whole from the tape.

Our children will need to think critically before attempting questions.

As such, our children need to realise that the tape length (25 m) cannot be divided equally by the required ribbon length (110 cm). Thus, they will need to figure out how many ribbons each tape can make.

So let’s try solving the question again.

How many of our children were tricked by this? Primary school Math is moving towards real life situations and application based questions; our children will need to think critically before attempting questions.

 

Let’s take this a step further by asking the question in another way to reinforce our kids understanding and application.

 

Our Modified Question


Jess wants 200 ribbons of length 110 cm for a party. The ribbons were sold at 25 m per tape.

(a) How many tapes will Jess need?
(b) If Jess decides to cut all the required tapes, how many 110 cm lengths of ribbon will she have in total?
(c) After cutting all the required tapes, Jess decides to join all the remaining unused ribbons, what will be its total length?

 

We can also ask the question in the following way to challenge them further.

 

Our Challenging Question


Jess wants 200 ribbons of length 110 cm for a party. The ribbons were sold at 25 m per tape.

(a) How many tapes will Jess need?
(b) What is the total length of all unused ribbon that Jess will have after cutting her 200 strips of 110 cm length ribbons? (Answer in meters)

Note: Part (b) is again a real life scenario that requires our children to understand that Jess will fully utilise the first 9 tapes and only cut the remaining ribbons she needs from the 10th tape.

 

 

Conclusion

It is more important to think through each question with a critical mind.

As you can see, Math questions are increasingly challenging these days. Blindly following key words to apply a certain methodology is becoming less useful. Hence, it is more important to think through each question with a critical mind.