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Question

What is the sum of the first n terms if the first term is 2, the common difference is 5 and the nth term is 122 in an arithmetic series?

A
1250
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B
1350
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C
1450
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D
1550
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Solution

The correct option is D 1550
First term: a=2
last term, l=122
d=5
an=a+(n1)d
122=2+(n1)5
1222+5=5n
125=5n
n=25
Sn=n2[a+l]
S25=252[2+122]
S25=12.5[124]
S25=1550

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