Question

13. Find the sum of:
(i) 1 +7 +13 + 19 to 40 terms.​

Answer 1

use the formula of Sn=n/2 (2a + (n-1)d)

and find the sum.

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Answer 2

Answer:

Sum of 40 terms is 4720

Step-by-step explanation:

Sum n=(n/2)(2a+(n-1)d)

her n is no. of term

a is first term and d is difference between 2nd and the 1st ter or 3rd and the 2nd term and so on

so after substituting the values

Sum 40=(40/2)(2×1+(40-1)6)

Sum 40=20(2+234)

Sum 40=20×236

Sum of 40 terms is 4720