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Question
In the following figure, a = 40°. The value of b is ______.

Options
20°
24°
36°
120°
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Solution
In the folllowing figure, a = 40°. The value of b is 20°.
Explanation:

From the given figure it is clear that,
2a + 5b = 180° ...[Linear pair]
⇒ 2 × 40° + 5b = 180° ...[∵ a = 40°]
⇒ 80° + 5b = 180°
⇒ 5b = 180° – 80°
⇒ 5b = 100°
⇒ b = `100^circ/5`
∴ b = 20°
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