Source: Complete International Mathematics For Cambridge IGCSE - David Rayner, Jim Fenson

 6.In triangle ABC,∠A is a right angle and D is a
point on AC such that BD bisects ∠B. If ∠BDC=100°, 
Calculate ∠C. 
 7.Triangles ABD, CBD and ADC are all isoceles.
Find the angle x.
 11.Two sides of a regular pentagon are produced
to form the angle x. What is x?
 12.Angle a is the interior angle of a
20-sided polygon. 
Angle b is the interior angle of a
15-sided polygon.
Calculate the value of angle c.

 13.The diagram shown is formed by joining
regular pentagons. Find the angles x and y.