# A family in Singapore part 17 (Math Question)

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The blog postings are about the Singapore Math. The readers can learn from the postings on Solving Singapore Primary School Mathematics. You or your kids can learn dealing with Math modeling, Problem Sum from Lower Primary School to Upper Primary School level in Singapore school. This posting is a primary school math question on Ratio, Average Number and Problem Solving.

You should read the posting on Sarin learns Average Number, Percentage and Charting in school (Math Concept) to understand the concept of Percentage and Charts.

Read also the posting on Sarin learns concept of ratio in school to understand the concept of Ratio.

Upper primary school mathematics question UPQ195

Sarin, Hairu and Fatimah weighed themselves with a bathroom scale. The average mass of the three kids was 72.6 kg. It was found that the bathroom scale measured certain weight without any person making measurement as the diagram shown. Given that Hairu is 2/3 of Sarin’s mass and Fatimah is 4/5 of Hairu’s mass, what is Fatimah’s actual mass?

Solution:

The reading on the scale is 5kg without making measurement.

The actual average mass = 72.6 – 5 = 67.6kg

Their actual total mass = 3 × 67.6 = 202.8kg

Draw the model of their mass ratio

From the model

33 units = 202.8

1 unit = 6.15 kg

Fatimah’s actual mass = 8 × 6.15 = 49.16 kg

Alternative solution:

The reading on the scale is 5kg without making measurement.

The actual average mass = 72.6 – 5 = 67.6kg

Their actual total mass = 3 × 67.6 = 202.8kg

The ratio of Hairu’s mass to Sarin’s mass = 2 : 3 = 10 : 15

The ratio of Fatimah’s mass to Hairu’s mass = 4 : 5 = 8 : 10

The ratio of Hairu’s mass to Sarin’s mass to Fatimah’s mass = 10 : 15 : 8

The actual mass in units = 10 + 15 + 8 = 33

1 unit = 202.8 ÷ 33 = 6.15 kg

Fatimah’s actual mass = 8 × 6.15 = 49.16 kg