# <span lang="EN-US

Given, first term a = – 5

Last term tn = 45

Sum of n terms Sn = 120

To find no of terms “n”

Using Sum of n terms of an A.P. formula where n = no. of terms

Sn = sum of n terms

Now, on substituting given value in formula we get,  120 = 20 n To find the common difference ‘d’

We use nth term of an A.P. formula

tn = a + (n – 1)d

where n = no. of terms

a = first term

d = common difference

tn = nth terms

Thus, on substituting all values we get,

t6 = – 5 + (6 – 1)d

45 = – 5 + 5d

5d = 45 + 5 = 50 Thus, common difference is 10

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