Let the first term, common difference and the number of terms of an AP are a, d and n respectively.
Given that, first term, a = - 5
last term, an = 45
Sum of the terms of the AP , Sn = 120
We know that, if last term of an AP is known, then sum of n terms of an AP is,
240 = 40n
n = 6
Also we know the nth term formula
an = a + (n - 1)d
45 = - 5 + (6 - 1)d
50 = 5d
d = 10
Hence, number of terms and the common difference of an AP are 6 and 10 respectively.
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