Q. If $\lbrack x\rbrack$ denotes the greatest integer $\leq x$, then $\left\lbrack \frac{2}{3} \right\rbrack + \left\lbrack \frac{2}{3} + \frac{1}{99} \right\rbrack + \left\lbrack \frac{2}{3} + \frac{2}{99} \right\rbrack + ... + \left\lbrack \frac{2}{3} + \frac{98}{99} \right\rbrack$ is equal to

A) 99
B) 98
C) 66
D) 65
Explanation

(c)
$\left\lbrack \frac{2}{3} + \frac{r}{99} \right\rbrack = \left\{ \begin{array}{r}
0,\ \ \ \ \ \ \ \ r < 33 \\
1,\ \ r \geq 33
\end{array} \right.\$
$\therefore\ \ \ \ \sum_{r = 0}^{98}{\left\lbrack \frac{2}{3} + \frac{r}{99} \right\rbrack = \sum_{r = 0}^{32}\left\lbrack \frac{2}{3} + \frac{r}{99} \right\rbrack + \sum_{r = 33}^{98}\left\lbrack \frac{2}{3} + \frac{r}{99} \right\rbrack}$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ = 0 + 66 = 66$

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

Ph.D. in Physics with 19+ years of teaching experience.