The mean of four consecutive even numbers is 15.the greatest of these numbers is a1.the least of these numbers is a2.

The greatest no a1 is 18 and smallest no a2 is 12

Step-by-step explanation:

Let the consecutive even numbers be

x, x+2 , x+4 , x+6

Given mean of four nos =15

Now mean = Sum of all observations/No of observations

15 =

4x +12 =15×4

4x + 12 = 60

Subtracting 12 both sides

4x + 12- 12 =60 - 12

4x = 48

Dividing both sides by 4

x=12

Hence the smallest no i.e. a2 is 12

Other nos be 12 +2 =14, 12+4 =16, 12 +6= 18

The greatest no i.e. a1 = 18

Hence the nos are 12, 14, 16, 18

m∠a is 90°

m∠b is 40°