A boy agrees to work at the rate of one rupee on the first day, two rupees on the second day, and four rupees on third day and so on. How much will the boy get if he started working on the 1st of February and finishes on the 20th of February?
A. 220
B. 220 -1
C. 219 -1
D. 219
E. None of these
Answer: Option B
Solution(By Examveda Team)
$$\eqalign{ & {1^{st}}\,{\text{term}} = 1; \cr & {\text{Common}}\,{\text{ration}} = 2 \cr & {\text{Sum}}\left( {{S_n}} \right) = a \times \frac{{ {{r^n} - 1} }}{{ {r - 1} }} \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 1 \times \frac{{ {{2^{20}} - 1} }}{{ {2 - 1} }} \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = {2^{20}} - 1 \cr} $$Join The Discussion
Comments ( 1 )
Related Questions on Progressions
Find the first term of an AP whose 8th and 12th terms are respectively 39 and 59.
A. 5
B. 6
C. 4
D. 3
E. 7
The sum of the first 16 terms of an AP whose first term and third term are 5 and 15 respectively is
A. 600
B. 765
C. 640
D. 680
E. 690
nth term=ar^n-1
2^19= 2^n-1
n=20
Sum=a(r^n-1)/r-1
=1(2^20-1)/2-1
=2^20-1