The fractions $\frac{1}{3}$ and $\frac{1}{5}$ have been placed on the number-line shown. At which position should the fraction $\frac{1}{4}$ be placed?
 
 
 
If you liked this problem, here is an NRICH task which challenges you to use similar mathematical ideas. 
 
 

This problem is taken from the UKMT Mathematical Challenges.