Using a common denominator \frac15 \qquad \frac14 \qquad \frac13\\
\\
\frac{12}{60} \qquad \frac{15}{60} \qquad \frac{20}{60}
The distance from \dfrac{12}{60} to \dfrac{20}{60} is \dfrac 8{60}
There are 16 intervals on the diagram so two make \dfrac1{60}
The distance from \dfrac{12}{60} to \dfrac{15}{60} is \dfrac 3{60} so go along 6 intervals
Finding the size of the intervals
The difference between \frac{1}{3} and \frac{1}{5} is \frac{1}{3}-\frac{1}{5}= \frac{2}{15}.
This section of the number line is divided into 16 intervals, each of length \frac{2}{15}\div 16 = \frac{1}{120}.
The difference between \frac{1}{4} and \frac{1}{5} is \frac{1}{4}-\frac{1}{5}= \frac{1}{20}= \frac{6}{120}, and hence \frac{1}{4}is six smaller intervals from \frac{1}{5}.