For a matrix $M=[m_{ij}]; \: i,j=1,2,3,4$, the diagonal elements are all zero and $m_{ij}=-m_{ji}$. The minimum number of elements required to fully specify the matrix is ________

The difference between the sum of the first $2n$ natural numbers and the sum of the first $n$ odd natural numbers is ______ $n^2-n$ $n^2+n$ $2n^2-n$ $2n^2+n$

The distance between Delhi and Agra is $233$ km. A car $P$ started travelling from Delhi to Agra and another car $Q$ started from Agra to Delhi along the same road $1$ hour after the car $P$ started. The two cars crossed each other $75$ minutes after the car $Q$ started. Both ... car $Q$. How many kilometers the car $Q$ had travelled when the cars crossed each other? $66.6$ $75.2$ $88.2$ $116.5$

The profit shares of two companies $P$ and $Q$ are shown in the figure. If the two companies have invested a fixed and equal amount every year, then the ratio of the total revenue of company $P$ to the revenue of company $Q$, during $2013-2018$ is ________. $15 : 17$ $16 : 17$ $17 : 15$ $17 : 16$

Two trains started at $7$AM from the same point. The first train travelled north at a speed of $80$km/h and the second train travelled south at a speed of $100$ km/h. The time at which they were $540$ km apart is ________ AM. $9$ $10$ $11$ $11.30$