Question
Mathematics Question on Combinations
Number of 4-digit numbers (the repetition of digits is allowed) which are made using the digits 1,2 , 3 and 5 , and are divisible by 15 , is equal to _____
Answer
The correct answer is 21.
For number to be divisible by 15, last digit should be 5 and sum of digits must be divisible by 3.
