Question

visualize 3.725 on a number line

Answer 1

see that 
 3.725 comes between 3 and 4 
3.725 comes between 3.7 and 3.8 
3.725 comes between 3.72 and 3.73  
  draw the number line AB where A=3.72 ,B=3.73
 and locate 3.725 on it

Answer 2

use the successive magnification method for this.it means first point out 3.7 between 3 and 4.after it mark 3.72 between 3.7 and 3.8. after it point 3.725 between 3.72 and 3.73. you can get the answer in ncert 9th maths textbook