Updated: Dec 4, 2019
Bars A, B and C are equal in size.
What fraction of all 3 bars is not shaded?
1. Find the common denominator of 3 and 4, which is 12. Each bar comprises 12 parts.
2. Since there are 3 bars, the total number of parts for all 3 bars = 12 x 3 = 36
3. Total number of shaded parts = 4 + 3 + 4 + 3 = 14
4. Total number of unshaded parts = 36 - 14 = 22
5. Fraction that is not shaded = 22/36 = 11/18
The learning point for this question is that students should not feel daunted the moment they see a question that looks more complicated than usual (see The "Unsolvable" 2019 PSLE Mathematics Question). After all, tenacity has solved more problems in the world than capricious flashes of brilliance.
The first step in problem-solving is reducing a problem to simpler terms. For example, if the question had simply asked for the fraction of unshaded part of A, or B, a typical Primary 3 student would not have batted an eyelid. C might have caused the student to pause in his or her tracks, but the student will eventually figure out that something needs to be done about the different denominators.
Indeed, once a student realises that each of the 3 bars can be divided into 12 parts, the battle is half-won.
As a parent, do you have difficulty imparting the virtue of tenacity to a nine-year-old?
Even after decades of teaching, we admit: so do we.
Why then, are we convinced that we can probably produce better results if you leave your child in our hands? The answer: teacher-student relationship and classroom dynamics. (We will cover this topic in detail if we get enough likes and shares for this article!)
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