Madhav ranks seventeenth in a class of thirty-one. What is his rank from the last?

Which number can be placed at the $(?)$ sign of interrogation?

$12 \left(47\right) 21, 10 \left(52\right) 4, 64 (?) 24$

Which number can be placed at the sign of interrogation?

Which number can be placed at the sign (?) of interrogation?

Fill up the missing number choosing from the following alternatives.

$3\times 2=10$

$4\times 3=14$

$5\times 4=18$

$6\times 5=22$

$7\times 6=?$