The tennis ball shown below can be put into the tube easily.
What do you think is the size (diameter, in cm) of the tennis ball ?
Let's use the letter d to represent the diameter of the tennis ball in centimetres (cm)
What are the possible values of d?

If d = 6.8, then the tennis ball may just fit the tube but its not easily to put in or take out!
So d could be 6.75, 6.7, or 6.6 or anything less than 6.8.
How do we write "d is less than 6.8 cm" mathematically? Well, d < 6.8
We were asking for the possible values of d which will allow the tennis ball to be put into the tube easily.
And the solution for d is : d < 6.8