to locate a point P on AB such that AP=5/3 AB line segment AB should be divided in the ratio :

A)3:5 B)5:3 explain the answer.... plsss fast

Since AP = 5/3 AB (fraction is greater than 1)  ..... This means that point P lies on the extended line AB(or say point P divides the line externally)
so we have to find the ratio in which point P divides AB 
A...........B............P
Now AP = 5/3 AB
      ⇒ AB+BP = 5/3 AB
     ⇒BP = 5/3 AB - AB
     ⇒BP = 2/3 AB

Now  AP = 5/3 AB and BP=2/3 AB
So ratio = AP/BP =(5/3)/(2/3)= (5:2)  (note:- here BP =PB as we are interested in length only)

Let us illustrate this with an example 
suppose Line AB is on the x-axis such that A has the cordinates(0,0), B has (3,0) and P has (5,0)  satisfying the conditions given in the question
so here AP/BP=5/2