For an A.P. the first term is 25 and 20th term is 500. Find the common difference.

Answer 1

a1 = 25

an = a1 + ( n- 1 ) d

a20 = a1 + ( 20 - 1 ) d

500 = 25 + 19 d Subtract 25 to both sides

500 - 25 = 25 + 19 d - 25

475 = 19 d Divide both sides by 19

475 / 19 = d

25 = d

d = 25