Riddle

What is the most useful instrument in a mathematics teacher's tool kit?

Choose an answer

A.A calculator
B.A ruler
C.A protractor
D.Multi-pilers!
Hint: It's a word with 11 letters, starting with "M".

Answer

Multi-pilers!

Why this is the answer

Pun on "multiplier," a math operation, sounding like "multi-piler."

This riddle is filed under Dirty, Family Riddles and rated Easy.