There are 18 points in a plane of which 5 are collinear. How many straight lines can be formed by joining them?

How many $3$ digit numbers can we make using the digits $4,5,7$ and $9$ and where repetition is allowed?

দৃশ্যকল্প-১ : 0, 5, 6, 7, 8 কতগুলো গাণিতিক অঙ্ক ।

দৃশ্যকল্প-২ : PROFESSOR শব্দটিতে নয়টি বর্ণ আছে

If $r, s$ and $t$ are prime numbers and $p, q$ are positive integers such that the LCM of $p,q$ is $\displaystyle r^{2}t^{4}s^{2}$ then the number of ordered pair $(p, q)$ is