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Question

The sum of first 10 terms and 20 terms of an AP are 120 and 440 respectively. What is the first term?

A
2
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B
3
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C
4
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D
5
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Solution

The correct option is C 3
Let the first term be a and common difference be d.
So, sum of first 10 terms =102(2a+(101)d)
120=5(2a+9d)
24=2a+9d .............. (i)
Sum of first 20 terms =202(2a+(201)d)
440=10(2a+19d)
44=2a+19d ......... (ii)
Subtracting equation (i) from (ii) gives
20=10d
d=2
Common difference =2
Substituting in (i), we get
a=3
Hence, option B is correct

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