Multiple choice

Find the sum of first $15$ terms of the sequence whose ${n}^{th}$ term is $3+4n$.

  1. $525$
  2. $425$
  3. $495$
  4. $None\,of\,thes$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The sequence is an AP with a = 3+4(1) = 7 and d = 4. Sum of n terms = n/2 * (2a + (n-1)d). For n=15: 15/2 * (2*7 + 14*4) = 15/2 * (14 + 56) = 15/2 * 70 = 15 * 35 = 525.

AI explanation

To find the sum of the first 15 terms of the sequence defined by the nth term 3 plus 4n, first identify the first and last terms of this specific sequence. The first term, found by substituting n equals 1, is 7, and the 15th term, found by substituting n equals 15, is 63. Using the arithmetic progression sum formula S equals n divided by 2 times the quantity a plus l, we calculate the sum as 15 divided by 2 times the quantity 7 plus 63, which equals 525.

Keep practicing — related questions