Sum of the first n terms of an AP is given by Sn = n/2 [2a + (n - 1) d].
Here, a is the first term, d is a common difference and n is the number of terms.
Given,
- First term, a = 5
- Last term, l = 45
- Sum of n terms, Sn = 400
We know that sum of terms of AP is given by the formula Sn = n/2 [a + l]
400 = n/2 (5 + 45)
400 = n/2 × 50
n = 16
By using the formula an = a + (n -1) d, we will find the common difference where an = l.
l = an = a + (n -1) d
45 = 5 + (16 -1) d
40 = 15d
d = 40/15
d = 8/3