If each term of a geometric progression $a_1, a_2, a_3, \ldots$ with $a_1=\frac{1}{8}$ and $a_2 \neq a_1$, is the arithmetic mean of the next two terms and $S_n=a_1+a_2+\ldots+a_n$, then $\mathrm{S}_{20}-\mathrm{S}_{18}$ is equal to
If each term of a geometric progression $a_1, a_2, a_3, \ldots$ with $a_1=\frac{1}{8}$ and $a_2 \neq a_1$, is the arithmetic mean of the next two terms and $S_n=a_1+a_2+\ldots+a_n$, then $\mathrm{S}_{20}-\mathrm{S}_{18}$ is equal to
- [JEE MAIN 2024]
- A
$2^{ \mathrm{15}}$
- B
$-2^{18}$
- C
$2^{18}$
- D
$-2^{15}$
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