Question

10. Sum the series 40+ 39 +38+ (C) 51 (D) 31 40 + 39 + 38+ + 11. (A) 780
(B) 775 (C) 765 CRE-2021/B (D) 820​

Answer 1

Answer:

answer is 775 option a of the question

Answer 2

Answer:

Sum of series 40 +39 +38 ... 11 = 765

Step-by-step explanation:

[The give problem might be about finding sum of the series

40+ 39 + 38..+ ..+ 11 ]

Given data  40 +39 +38..+ + 11

here first term of series  a = 40

the series is in AP or Arithmetic Progression

and common difference  d = T₂ - T₁ = 39 -40 = -1

the number of terms =  40 -11+ 1 = 30

sum of the n terms = $\frac{n}{2}$ [ 2a (n-1) d]

sum of 30 terms  = $\frac{30}{2}$ [ 2(40)+ (30-1) (-1)]

                             = 15 [ 80 +(29)(-1)]

                             = 15 [ 80 -29]

                             =  15 [51] =  765