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