Answer:
n = 24
Step-by-step explanation:
From the question,
The formula for the sum of the term in an AP is given as
Sₙ = n(a+L)/2.................. Equation 1
Where Sₙ = sum of the nth term, n = number of term, a = first term, L = last term.
make n the subject of the equation
n = 2Sₙ/(a+L)................. Equation 2
Given: Sₙ = 420, a = 4, L = 31
Substitute these values into equation 2
n = (2×420)/(4+31)
n = (840)/35
n = 24.
Hence, n = 24
