The 10th and 15th terms of an AP are -5 and 7 1/2 respectively.What is the sum of the first 20 terms
6 answers
solve this and let me know your workings because the answer is -105
the common difference is d = (7 1/2 + 5)/5 = ____
a = -5 - 9d = ___
S20 = 20/2 (2a+19d) = ___
a = -5 - 9d = ___
S20 = 20/2 (2a+19d) = ___
Not enough workings
Answer is -105. a+9d=-5.
a+14d=-7^1/2.a=-1/2.,d=-1/2.
a+14d=-7^1/2.a=-1/2.,d=-1/2.
10th "B"
55
2 answers