Single Choice

How many terms of the series $$1+3+9+ ...$$sum to $$121$$?

A$$5$$
Correct Answer
B$$6$$
C$$4$$
D$$3$$

Solution

The given series is a G.P
Sum of n terms of a G.P is $$ a* {(\frac{(r^n\;-\;1)}{(r-1)})} $$
Here a=1 and r=3
Substituting it in the equation and finding n we get n=5

SIMILAR QUESTIONS

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