PSLE Maths TOTW ~ All About Estimation


The following Multiple-Choice Question (MCQ) appeared in the 2015 PSLE Mathematics paper.

Which of the following is likely to be the total mass of 8 one-dollar coins?

  • 6 g

  • 60 g

  • 600 g

  • 6000 g

Questions such as this are not meant to promote a feverish trend of students measuring and memorising random data in their everyday life. Instead, they are designed to force students apply textbook knowledge in the context of their everyday lives. Through such questions, the gram is promoted from simply being an abstract symbol attached to numerical values in word problems, to being practical units of measurement in real life.

To answer this MCQ, students will try to recall familiar reference objects with masses close to the four options. For example, at the supermarket, if students had paused for a second to feel the weight of a 500-g packet of sugar, they would be able to rule out 600 g and 6000 g as the answers. In deciding between 6 g and 60 g, they might recall that a 9-g sachet of ketchup at McDonald's felt almost weightless in their hand.

However, bear in mind that familiarity does not automatically mean cognizance, for one may have squeezed out countless sachets of McDonald's ketchup without ever knowing what one sachet actually weighs. What students should do is to actively develop their natural inquisitiveness so that they become a more conscious observer of the world around them. That way, when the situation calls for it, they will be able to make associations among various objects more easily.

So there you have it: one more excuse to make your children carry your groceries on your next shopping trip. It'll be no exaggeration to tell them it's for their own good!

Have a go at next four MCQs, extracted from a Joyous Learning Maths worksheet (Mad Maths section).

  1. Which of the following is likely to be the ratio of the area of a two-dollar note to the area of a sheet of A4-sized paper? (a) 1 : 4 (b) 1 : 8 (c) 1 : 16 (d) 1 : 32

  2. Which of the following is likely to be the ratio of the area of an EZ-Link card to the area of a sheet of A4-sized paper? (a) 1 : 3 (b) 1 : 7 (c) 1 : 13 (d) 1 : 19

  3. Which of the following is likely to be the ratio of the area of a table-tennis table to the area of a badminton court? (a) 1 : 2 (b) 1 : 20 (c) 1 : 200 (d) 1 : 2000

  4. Which of the following is likely to be the ratio of the length of a motorcycle to the length of a double-decked public bus? (a) 1 : 5 (b) 1 : 10 (c) 1 : 15 (d) 1 : 20

Heuristics for estimation to help students arrive logically at the correct answer are taught as part of this lesson.

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