NumericalModerate2 marks
2(c)
In an Arithmetic Progression (A.P.) the fourth and sixth terms are 8 and 14 respectively. Find the:
sum of the first 20 terms.
Topic: Arithmetic progression
Previous-year question practice database
Answer
Exam answer
From earlier parts: a = −1, d = 3.
S₂₀ = 20/2[2(−1)+19(3)] = 10(−2+57) = 550.
Answer: 550.
Explanation
Use Sₙ=n/2[2a+(n−1)d] with the first term and common difference already obtained.