Calculating Angles at a Point and on a Straight Li...
• Introduction

Angles at a point add to 360°.

Angles on a straight line add to 180°.

If we know one of the angles at a point, or on a straight line, we can calculate the other one.

Examples

 At a point:   a + 240° = 360° a = 120° On a straight line:         b + 160° = 180° b = 20° At a point:     a + 45° = 360° a = 315°
• Question 1

Calculate the unknown angle.

a = 120

a = 120°

a = 60°

• Question 2

Calculate the unknown angle.

a = 220°

a = 120°

a = 315°

• Question 3

Calculate the unknown angle.

b = 40°

b = 20°

b = 15°

• Question 4

Calculate the unknown angles, c and d.

 120° 90° 100° c d
• Question 5

Calculate the unknown angle.

a = 140°

a = 110°

a = 115°

• Question 6

Calculate the unknown angle.

a = 325°

a = 210°

a = 245°

• Question 7

Calculate the unknown angle.

a = 85°

a = 90°

a = 45°

• Question 8

Calculate the unknown angle.

b = 55°

b = 55

b = 45°

• Question 9

Calculate the unknown angle.

b = 55°

b = 180°

b = 25°

• Question 10

Calculate the unknown angles, c and d.

 140° 60° 40° c d
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