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Sequences and Series — Maths STD 11 Science — Question

CBSE BoardEnglish MediumSTD 11 ScienceMathsSequences and Series1 Mark
MCQ
In $G.P.\ 4, 8, 16, 32, …$ find the sum up to $5^{th}$ term.
  • A
    $16$
  • B
    $64$
  • C
    $128$
  • ✓
    $124$
✓

Answer

Correct option: D.
$124$
In the given $\text{G.P.}$
$=4$ and $\text{r}=\frac{8}{4}=2.$
We know, $\text{s}_\text{n}=a\frac{\text({r}_\text{n}-1)}{\text({r}-1)} $
$\Rightarrow{\text{s}}_5$
$=4\frac{(2^5-1)}{(2-1)}$
$=4\times31$
$=124.$
 

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