## BdMO National 2013: Primary 5

BdMO
Posts: 134
Joined: Tue Jan 18, 2011 1:31 pm

### BdMO National 2013: Primary 5

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
Posts: 1007
Joined: Sat Dec 09, 2017 1:32 pm

Hint