Question

yhe first term of ap is - 5 and the last term is 45 and the sum of their terms is 120. Find the difference aand the number of terms??
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Answer 1

Answer:

sum of terms=n/2(a+l)

120=n/2(-5+45)

n×40=120×2

40n=240

n=6

an=a+(n-1)d

120=-5+5d

125=5d

d=125/5

d=25