Sarin learns Perimeter, Area and Volume in school part 57 (Math Question)

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The blog postings are about the Singapore Math. The readers can learn from the postings about 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 can learn deal with Math Modeling, Problem Sum from Lower Primary School to Upper Primary School level. This posting is an upper primary school math question on Fraction, Area and Perimater.

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

Read also the posting on Sarin learns the concept of Fraction (mathematics concept) to understand the concept of Fraction.

Upper primary school mathematics question UPQ223

The figure below has shown an octagon fit exactly into a circle. The area of the circle is 616cm2. Assume the value π = 22/7, to find the area of the orange shapes.

Solution:

The area of the circle = π × r × r = 616 cm2

r × r = 616 × 7/22 = 196 = 14 × 14

The radius of the circle, r = 14cm

Subdivided the octagon with dotted lines shown

The area of the green triangle = ¼ fraction of the square with green dotted outline

The area of the square with green dotted outline = 4 × ½ × 14 × 14 = 392 cm2

L × L = 392

The length of the square with green dotted outline = 19.80 cm

The ¼ fraction of the octagon = Sum of the area of the green triangle and blue triangle

The area of the octagon = 4 × 14 × 19.8 ÷ 2 = 554.4 cm2

The area of the orange shapes = 616 – 554.4 = 61.6 cm2