The oldest child in a family of four children is twice as old as the yougest. The two middle children are 12 and 15 years old. If the average age of the children is 12.75 , how old is the youngest child?

8 years old

Step-by-step explanation:

oldest= 16

8+12+15+16= 51

51/4 = 12.73 ( average)

∠acb = 8°

step-by-step explanation:

∠xba lies on the circle and is half the measure of the intercepted arc ax

hence

measure of arc ax = 2 × 42° = 84°

∠acb is outside the circle and is

∠acb = (arcab - arcax ), hence

∠acb = 0.5 (100 - 84) = 0.5 × 16° = 8°