The refractive index of the diamond is $2.41$. What is the speed of light in a diamond?

Represent the union of two sets by Venn diagram for each of the following.

$X=\{x | x$ is a prime number between $80$ and $100\}$

$Y=\{y | y$ is an odd number between $90$ and $100\}$

What shape a sphere will appear to have when it is carried by a very fast moving person?

The guru of a yogi lives in a Himalayan cave, $600000 \mathrm{km}$ away from the house of the yogi. The yogi claims that whenever he thinks about his guru, the guru immediately knows about it. Calculate the minimum possible time interval in seconds between the yogi thinking about the guru and the guru knowing about it.