What algebraic expression is obtained by subtracting the quotient of $x \mathrm{by} y$ from the product of $x \mathrm{and} y?$ 
 

In a competition, $35$ students appeared in an examination. Only $20$ students passed the examination. 
What is the ratio of passed students to the failed students 
 

Mention the name of mathematical instruments present in the geometry box and their uses.