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, August 22, 2010

RGS Primary 2009 PSLE Math Prelim Paper 2 Q8

In the figure below, O is the centre of the circle where OCD is an equilateral triangle. Given that Angle OAB = 20 degrees and Angle AOD = 127 degrees, find Angle BOC.


Solution


Angle DOC --> 60 degrees (Triangle OCD is equilateral)
Angle AOB --> (180 - 20 - 20) degrees
= 140 degrees (Triangle OAB is isosceles)

Angle BOC --> (360 - 140 - 127 - 60) degrees
= 33 degrees

Answer: 33 degrees

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