Q. 455.0( 1 Vote )

# How many terms of the G.P. 3, 32, 33, …… are needed to give the sum 120?

Given : 3 + 32 + 33+ ….. = 120

Now a = 3, r = 3. Let number of terms = n

Also = 120
or = 120

or 3n – 1 =

or 3n – 1 = 80

or 3n = 81 = 34

Hence n = 4

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