Total number of pencils = 500
The shop sold 3 sets of 20 coloring pencils = (3*20)
The shop sold 6 sets of 12 coloring pencils = (6*12)
The shop again sold 10 sets of 18 coloring pencils = (10*18)
So, the expression for the number of coloring pencils that are left consider the order of operations:
= 500 - (3*20) - (6*12) - (10*18)
On solving we get:
= 500 - 60 - 72 - 180
= 500-312
=188
Number of coloring pencils left = 188