arithmetic problem

Jan 2008
173
1
On the first day, Nabil put $1 in a big box. Then, each succeeding day, he added to the box exactly twice as many dollars as he did on the previous day. On which day will Nabil have more than $1000 in his box for the first time?

(A) 8th day (B) 9th day (C) 10th day (D) 11th day (E) 1000th day


 
Jun 2009
806
275
On the first day, Nabil put $1 in a big box. Then, each succeeding day, he added to the box exactly twice as many dollars as he did on the previous day. On which day will Nabil have more than $1000 in his box for the first time?

(A) 8th day (B) 9th day (C) 10th day (D) 11th day (E) 1000th day
Sum S = 1 + 2 + 4 + ..........

It is geometric series.

S = a(r^n - 1)/(r-1)

Here a is the first term r is the common ratio and n is the number of days.

S, a and r is given.

Can you find n?