Counting Restrictions from Glyia
Very nice introductory level counting questions with restrictions.
from Mathcounts Mini : Counting the Number of Subsets of a Set
from AoPS :
Counting with Restrictions Part 3 : This one is tricky. Make sure you understand the concepts well.
Try this question from 2011 AMC-8 # 23 :
How many 4-digit positive integers have four different digits, where the leading digit is not zero, the integer is a multiple of 5, and 5 is the largest digit?
Solutions from AoPS
Counting with Combinations Part 3
At our group lessons, we'll continue working on harder Mathcounts concepts, not just the accuracy, but speed.
Take care and happy problem solving !!