BdMO National 2013: Primary 5

[BdMO]

For any two numbers $x$ and $y$, the absolute value of $x$ and $y$ is defined as $|x-y| = $ difference between the numbers $x$ and $y$. For example, $|5-2| = 3, |3-9| = 6$. Let $a_1, a_2, a_3, \cdots , a_n$ be a sequence of numbers such that each term in the sequence is larger than the previous term.

Let $S = |a_1 - a_2| + |a_2 - a_3|+ \cdots + |a_{n-1} - a_n|$. What is the minimum number of numbers that you need to know from the sequence in order to find $S$?

[samiul_samin]

Hint

Use numberline and read the question twice

Answer

$\fbox 2$

Inspired by Afser_Adil_Olin