How can we write an expression to show 3 less than a number?

 Start by drawing a diagram to model the subtraction. Are we taking away from the 3 or the unknown number?

 What expression would represent this model?

x - 3

Step-by-step explanation:

Let x be the unknown number,

For making the diagram to model this problem,

Take a grid that shows x,

Divide this grid into two parts,

If first part is of 3 then second part would be x - 3

That is, we are taking away 3 from the unknown number,

Hence, the required expression would be x - 3