Step-by-step explanation:

Let 1:3 be x and 3x

in which:

x = coloured chalks

3x = white chalks

Given that:

no. of white chalks used were - 60

so equation formed is:

3x = 60

solution of equation:

3x = 60

x = 20

x = 20 = coloured chalks

therefore the number of coloured chalks used were 20.