Question

what is the sum of 1st 20 terms of the progression 10,15,20.....than the next 20 terms?

Answer 1

Common difference = 15 - 10 = 5

1 st term = 10 = a

20 th term = a + 19(d)
20th term = 10 + 19(5) = 10+95 = 105

=================

S(n) = [ first term + last term] × n/2

S(20) = [ 10 + 105] × 20/2

S(20) = 115 × 10

Sum of 1st 20 terms = 1150



I hope this will help you

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Answer 2

Heya !!!

AP = 10 , 15 , 20 ........ 20

Here,

First term ( A) = 10

Common Difference (D) = 5

Therefore,

Sum of first 20 terms =

=> Sn = N/2 × [ 2A + ( N-1) × D ]

=> S20 = 20/2 × [ 2 × 10 + (20-1) × 5) ]

=> 10 (20 + 19 × 5)

=> 10 ( 20 + 95)

=> 10 × 115

=> 1150.

HOPE IT WILL HELP YOU...... :-)