This blog is managed by Song Hock Chye, author of Improve Your Thinking Skills in Maths (P1-P3 series), which is published and distributed by EPH.

Sunday, June 29, 2008

Ai Tong School P6 SA1 2006 Math (Q48)

The figure below shows a circle and two quadrants enclosed within a square. O is the centre of the circle. Find the total area of the shaded parts in the figure shown. (Take =3.14)



Solution

Redrawing…..



Area of A ----- Area of small square – Area of small quadrant

= (10 cm x 10 cm) – (3.14 x 10 cm x 10 cm x ¼)
= 100 square cm – 78.5 square cm
= 21.5 square cm


Area of 1 shaded portion ----
Area of large square – Area of large quadrant – Area of A

= (20 cm x 20cm) – (3.14 x 20 cm x 20 cm x ¼) – 21. 5 square cm
= (400 – 314 – 21.5) square cm
= 64.5 square cm

Area of total shaded portion therefore is 64.5 square cm x 2 = 129 square cm (Answer)

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