Average acceleration given three velocity vectors?

[Esoremada]

Can someone explain this? http://puu.sh/4LNE6.png

What is the relevance of t₁ < t₂ < t₃

 

[mfb]

t1<t2<t3 just makes sure your time-ordering is right, so you first have v1, afterwards v2, and then v3, and not some other order.

 

[Esoremada]

Oh I was thinking of them each representing time intervals for some reason, I get it. Thanks