The sum of the 1st five terms of a
geometrical progression is 484. If the common ratio is 3 find the 4th term.
solution
S5 = 484,
G1 = ?, r=3, n=5, A2=?
We use the summation formula to find
the 1st term.
Sn = G1(rn-1)/r-1
S5 = G1(r5-1)/r-1
484= G1(35-1)/3-1
484= G1(243-1)
2
2 x 484= G1(242)
968= 242 G1
4 968 =
G1
G1 = 4
Now we solve for the 2nd
term.
Gn = G1rn-1
G4 = G1r4-1
G4= G1r 3
G4 = 4 x (3)3
= 4 x 27
= 81
Hence the 4th term is 81.
TRY THIS.........................
The sum of the 1st five terms of a geometrical
progression is 484. If the common ratio is 3 find the 3rd term.
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