Using Average formula,
Jack's average for second nine weeks is 77.
Average: Average of observations is fraction of sum of observations values to the total number of observations.
Mathematically, Average = ∑ X/ n
where, X ---> observations values
n --> total number of observations taken
We have given that ,
Average for first nine weeks of Jack's marks in maths (A₁) = 88
i.e sum of marks in maths obtained by jack
= 88×9= 792
Also have , Average of jack's marks in maths for second nine weeks (A₂ ) is decreased by 12.5% from first nine weeks.
In Mathematically, A₂ = A₁ - 12.5% of A₁
=> A₂ = 88 - 12.5%of 88
=> A₂ = 88 - (125/100)88
=> A₂ = 88 - 11 = 77
Hence, Jack's average for second nine weeks is 77.
To learn more about Average, refer:
https://brainly.com/question/24233224
#SPJ4
