Asked by Maths

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