Singapore Math Guru

PSLE question on Weight Of $1 Coins

Just recently, parents and students went berserk over a question asking students to estimate the weights of coins. So the question went something like this.

How heavy are eight $1 Singapore coins?

(a) 6 g

(b) 60 g

(c) 600 g

(d) 6 kg

A question like this tests a students’ ability to estimate masses of common objects, in this case, masses of $1 coins. Also another skill a student must have here is to eliminate the wrong options to get the correct answer. So estimation and elimination skills are required for such a question and it is not unreasonable that MOE and Singapore Examinations & Assessments Board tested the question.

Firstly, I think any reasonable person would cross out 6 kg as an answer.

So the student should have done this.

(a) 6 g

(b) 60 g

(c) 600 g

(d) 6 kg

 

6 kg is definitely out. 6 kg is the mass of some weights out there in the gym. That can be rather heavy for 8 $1 coins don’t you think? So here, a student has just eliminated 1 option. And that leaves 3 options. So elimination is a very important skill here.

Could 600 g be the answer? If you cook, you will find that 600 g for the mass of 8 coins would be an overestimation. Also, half-filled 1 liter bottles already have masses of approximately 500 g. If you take 600 and divide it by 8, it is 75 g. Can 1 $1 coin have a mass of 75 g? Low probability and likelihood. So cross that one out.

(a) 6 g

(b) 60 g

(c) 600 g

(d) 6 kg

So it is now down to 2 options. It is either 6 g or 60 g and you would have to make a good guess if you still don’t know. But at least, you have narrowed down the answer to 2 possible options and you have a higher chance of getting it correct. Common sense will tell us that 6 g is too light and hence 60 g is the answer.

psle2015weight$1coins