# Sarin, Hairu and Fatimah make greeting cards for Mother’s Day part 14 (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. The blog presenting the Math Concept, Math Questions with solutions that teaches in Singapore Primary Schools. You or the kids will learn the skill of dealing with Math Question Solving, Math Modeling and Problem Sums from Lower Primary School to Upper Primary School level. This posting is an upper primary school math question on Shape and Area.

You can read the story of Sarin and the siblings making greeting cards for their mother by reading the posting on Sarin, Hairu and Fatimah make greeting cards for Mother’s Day in Welcome page.

You can read the posting on Sarin learns Perimeter, Area and Volume in school(Math Concept) to learn the concept of perimeter, area and volume.

Read also the posting on Sarin learns Shapes and Solids in school (Math Concept) to know about shapes.

Upper primary school mathematics question UPQ232

Sarin’s mother received a greeting card from Sarin. It is a special design shape card as the figure below. The card design was a rectangle with two corners being cut out. The cut out are identical isocelete triangles. It the area of the shape was 189.6cm2,what is the area of one cut out triangle?

Solution:

Every cut out is an isocelete triangle at the corner of the rectangle. It will have two equal sides of length B as shown in the figure and is a right-angle triangle.

So the area of the blue triangle in the figure is equal to the area of the cut out triangle.

By rearrange the shape, we have the area of the shape is the sum of the area of three rectangles.

The area of the big rectangle = 6 × 18 = 108cm2

The sum of area of the two smaller rectangles = 189.6 – 108 = 81.6cm2

Both the small triangles have the same breath = B

6B + 18B = 81.6

B = 81.6 ÷ 24 = 3.4cm

The area of one cut out triangle = 3.4 × 3.4 ÷ 2 = 5.78cm2