The blog postings are about the Singapore Math. The readers can learn from the postings about Solving Singapore Primary School Mathematics. The blog presents the Math Concept, the Math Questions with solutions that teaches in Singapore Primary Schools. You or the kids can learn the skills to deal with the Math Modeling, the Math Problem Solving and the Problem Sum from Lower Primary School to Upper Primary School level after reading the blog postings. This posting is an upper primary school math question on Problem Solving.

Read the posting on **Sarin participates in school anniversary event part 1 **for story on school anniversary.

*Challenge yourself with the question before look out for the given solution‼*

**Upper primary school mathematics question UPQ486**

To prepare for the school anniversary event, Sarin spent a total of $69 on some rulers, pens and erasers. 25% of them were rulers and cost 90₵ each. The number of pens was 6 more than half the total number of items and the remaining were erasers. If a pen cost $2.20 and an eraser cost 70₵, find the total number of pens Sarin bought.

Solution:

The model based on quantity,

Convert the model based on cost

The cost of one ruler = $0.90

The rulers ==> 1 units ==> 1 × 0.9 = 0.9 unit

The cost of a pen = $2.20

The pens ==> 2 units + 6 ==> 2 × 2.2 units + 6 × 2.2 = 4.4 units + 13.2

The cost of an eraser = $0.70

The erasers ==> 1 units – 6 = 1 × 0.7 units – 6 × 0.7 = 0.7 unit – 4.2

The total cost ==> 0.9 unit + 4.4 units + 13.2 + 0.7 unit – 4.2 = 6 units + 9

The cost model,

6 units + 9 = $69

6 units = 60

1 unit = $10

The total cost of the pens = 4.4 × 10 + 13.2 = $57.2

The total number of pens = 57.2 ÷ 2.2 = 26

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