Discussion Forum

Daily Magic Spell Discussion - January 2, 2017

 
 
Institute Areteem的相片
Daily Magic Spell Discussion - January 2, 2017
Institute Areteem發表於2017年 02月 23日(Thu) 10:12
 

Today, we will discuss about the Daily Magic Spell problem given on January 2, 2017:

Problem: Find the value of $\displaystyle \frac{20!-19!}{18!}$.

Solution: Note that

$\displaystyle \frac{20!-19!}{18!} = \frac{20(19!) - 19!}{18!} = \frac{19(19!)}{18!} = 19\times 19 = 361$.

Some students may attempt to evaluate $20!$, $19!$, and $18!$ naively. Although this could yield the correct answer, the approach itself requires too much effort to solve the problem.

If you have any other approaches that you would like to share with us, feel free to post and let us know how you would tackle this problem! We would like to hear your thoughts!