Question

Find the sum of 15 terms from the end of the AP: 3,8,13,.....,253.​

Answer 1

Given:

• a = 3
• d=5
• a(n) = 253

Solution:

• After reversing the A. P. we get, 253,.....13,8,3
• Here we get
• a = 253 , d = -5 , a(n) = 3
• $s15 = \frac{15}{2} (253 + 3)$
• s(15) = 7.5×256
• = 1920

Hope it helps!