Arithmetic Series Word Problem(Easy)?

Comments

• raj-k

  May 2021

  Second term =40

  Fifth term = 121

  Let first term = A

  and common difference = d

  Secon term = A+d =40......(i)

  and Fifth term= A+4d=121.....(ii)

  Solving (i) and (ii) gives d= 27 and A=13

  Sum of First n terms =(n/2){2A+(n−1)d}

  Sum of First 25 terms =(25/2){2×13+(25−1)×27}=8425
• barnali

  May 2021

  For A.P series formula for nth term

  is t_n = a + (n-1)d, where a is first term and d is common difference.

  t_2 = 40

  or, a + (2-1)d = 40

  or, a + d = 40.......................(1)

  t_5 = 121

  or, a + (5-1)d = 121

  or, a + 4d = 121..................(2)

  now solving (1) and (2) we get

  a = 13 and d = 27.

  Formula for sum of n terms of an A.P series is

  S_n = (n/2)[2a+(n-1)d]

  Here, a=13, d=27, n=25

  So, Sum of 25 terms is

  S_25 = (25/2)[2*13+(25-1)27]

  =8425
• anotheropinion

  May 2021

  8425