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A boy agrees to work at the rate of 1 rupees on the first day, 2 rupees on the second day. Four rupees on the third day and so on . how much will the boy get if he starts working on the 1st of February and finishes on the 20th of February ?
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- 220
- 220-1
- 219-1
- 219
Correct Option: B
According to given question,
First day 1 rs, second day 2 rs, third day 4 rs.....
1 , 2 , 4............ and so on
The given series is in geometric progression (GP).
1, 21, 22,.............
Sum of first n terms in a geometric progression(GP)
Sn = a (rn ? 1) /(r ?1)
if r > 1 and where a= the first term, r = common ratio,n = number of terms
As per the given question a = 1 , r = 2 and n = 20;
Sn = 1(220 ? 1) /(2 ?1)
Sn = (220 ? 1) /1
Sn = (220 ? 1)
Sn = 220 ? 1
