This question is based on basic counting.
87956
10-digit numbers with constraints
48502
number of ordered pairs of integers $(x,y)$ satisfying the equation
26343
Number of certain (0,1)-matrices, Stanley's Enumerative Combinatorics
14235
count vs length vs size in a collection
96585
Sums and permutation
134599
How do I do Combinatorics / Counting?
113331
Number of ways a natural number can be written as sum of smaller natural number
90068
Calculating the number of times a digit is written when given two numbers
150281
Am I on the right track to figure out this combinatorics problem?
103089
Count and use the number of items in advance
41448
Counting set for generating functions
145712
The amount of VS The number of, etc
60915
Count number of 1's in binary representation
18429
Counting measure proof
11460
Expected count of correct assignments
94634
How many times more than $0$?
26569
Counting binary operations on a set with $n$ elements