What is the sum of the first 15 terms of an A.P whose 11 th and 7 th terms are 5.25 and 3.25 ...
What is the sum of the first 15 terms of an A.P whose 11 th and 7 th terms are 5.25 and 3.25 respectively
Answer/Solution
56.25
Steps/Work
a +10d = 5.25, a+6d = 3.25, 4d = 2, d = ½
a +5 = 5.25, a = 0.25 = ¼, s 15 = 15/2 ( 2 * ¼ + 14 * ½ )
= 15/2 (1/2 +14/2 ) = 15/2 *15/2 =225/ 4 = 56.25
ANSWER:A
a +5 = 5.25, a = 0.25 = ¼, s 15 = 15/2 ( 2 * ¼ + 14 * ½ )
= 15/2 (1/2 +14/2 ) = 15/2 *15/2 =225/ 4 = 56.25
ANSWER:A