Question

Find the sum of following series 1,4,7,10 to 20 terms

Answer 1

Answer:

I think your answer is 1777

Step-by-step explanation:

sum of (1,4,7,10,11 ,12,13,14,15,16,17,18,19,20)

Answer 2

The sum of 20 term of an A.P. is 590

Step-by-step explanation:

GIVEN

a = t1 = 1

t2 = 4

t3 = 7

t4 = 19

nth term = 20

___________________________

We know that,

Common Difference ( d ) = t2 - t1

Common Difference ( d ) = 4 - 1

Common Difference ( d ) = 3

Common Difference ( d ) = 3

___________________________

We know that,

Sn = n/2 × [ 2a + ( n – 1 ) d ]

S20 = 20/2 × [ 2 × 1 + ( 20 - 1 ) 3 )

S20 = 20/2 × [ 2 + 19 × 3 ]

S20 = 20/2 × [ 2 + 57 ]

S20 = 20/2 × 59

S20 = 20/2 × 59

S20 = 10 × 59

S20 = 590

The sum of 20 term of an A.P. is 590