It is a GP. with r = 2, ie \begin{aligned} 2^1, 2^2, 2^3... \end{aligned}
If number of terms is n. Then,
\begin{aligned} 2 \times 2^{n-1} = 1024 \end{aligned} =>
\begin{aligned} 2^{n-1} = 512 \end{aligned}
or \begin{aligned} 2 \times 2^{n-1} = 2^9 \end{aligned}
so n-1 = 9 => n = 10
2. 587 * 999 = ?
586411
586413
486411
486413
Answer: Option B
Explanation:
Trick: 587 * (1000 - 1) = 587000 - 587 = 586413
3. Simplify 586645 * 9999
5865863355
5665863355
4865863355
4665863355
Answer: Option A
Explanation:
Although it is a simple question, but the trick is to save time in solving this.
Rather than multiplying it we can do as follows:
586645 * (10000 - 1) = 5866450000 - 586645 = 5865863355