The average age of staff in the maths department is 40. There are 7 members of staff (Jill, Nicky, Wendy, Cathy, Cerian, Alan and Andy).

The average age of Jill, Nicky and Wendy is 41.

The average age of Andy, Alan and Cathy is 43.

How old is Cerian?

Cerian is 28 years old

Step-by-step explanation:

The given parameters are;

The average age of the staffs in the mathematics department = 40

The number of staffs in the department = 7

The average age of Jill, Nicky and Wendy = 41

The average age of Andy, Alan and Cathy = 43

From the given parameters, we have;

The average age of the staffs in the mathematics department = (The sum total of the ages of the members of the math department)/(The number of staffs in the department)

Therefore;

40 = (The sum total of the ages of the members of the math department)/ (7)

From which we have;

The sum total of the ages of the members of the math department = 40 × 7 = 280

Which gives;

Jill's age + Nicky's age + Wendy's age + Cathy's age + Cerian's age + Alan's age + Andy's age = 280 years

The average age of Jill, Nicky and Wendy = 41

Given that Jill, Nicky, and Wendy make up 3 of the 7 members of staffs, we have;

The average age of Jill, Nicky and Wendy = (The sum total of the ages of Jill, Nicky, and Wendy)/(The number of staff Jill, Nicky, and Wendt make)

Therefore;

The sum total of the ages of Jill, Nicky, and Wendy = 41 × 3 = 123

Which gives;

Jill's age + Nicky's age + Wendy's age = 123 years

Similarly, the sum total of the ages of Andy, Alan, and Cathy = 43 × 3 = 129

Which gives;

Andy's age + Alan's age + Cathy's age = 129 years

Therefore;

Cerian's age = (Jill's age + Nicky's age + Wendy's age + Cathy's age + Cerian's age + Alan's age + Andy's age) - (Jill's age + Nicky's age + Wendy's age) + (Andy's age + Alan's age + Cathy's age)

∴ Cerian's age = 280 years - 123 years - 129 years = 28 years

gregory's graph is incorrect because it shows 2 inches of growth for each week when it should show 0.75 inches of growth each week.