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

Step-by-step solution

Given, We have to form four-digit number using the digits 1 ,   2 ,   3   &   5 Now for number to be divisible by 15 we need to fix the last digit as 5 as _   _   _   5 , so that number can be divisible by 5 and for divisibility by 3 the addition of all number should be divisible by 3 , So making cases where sum is divisible by 3 we get, Case 1 -   1 , 1 , 2 as  1 ,1,2 & 5  sum is divisible by  3 So, total ways for case 1 is 3 w