# Bar Model Approach to PSLE-2019 Questions

Ho Soo Thong

Revised Nov 2021

In 2019 PSLE Examination, pupils encountered quite a number of challenging questions.

Here, we intend to highlight the basic mathematics in a *Holistic Bar Modelling Approach* to two types of challenging questions :

Ratio (fraction) situations – A Counting Approach with the *Greatest Common Unit*

Distributive Situations – Mathematics of *Distributive Law*

A holistic bar model enables us to understand each question and select an effective approach to the solution. Furthermore, we can see the challenging level of each question.

**Question 1 **PSLE 8/02/2019

A box contained black beads and white beads. At first, the number of black beads was ⅓ of the number of white beads. After ¼ of the black beads and ⅜ of the white beads were used,63 beads were left.

(a)What is the fraction of the beads were used? Leave your answer in the simplest form.

b)How many beads were there in the box at first?

Solution

*Remark* : The question involves three related “Fraction”situations. There is a complex algebraic relation 3X = 8Y for which we apply the *Greatest Common Unit Procedure *for a counting approach.

**Question 2 **PSLE 14/02/19

Kelvin and Julie bought some egg tarts. Each of them spent $61.20. Julie got 6 more egg tarts than Kelvin because she used a coupon that gave her a 15% discount.

(a) How many egg tarts did Julie get?

(b) What was the price of each egg tart without the discount?

Solution

*Remark *: A challenging *Distributive Problem* involves the algebraic relation

*Total cost = Unit cost × Number of units. *

The question can be solved as a *Percentage Problem* and here we show a direct* ratio approach*.

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