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
Explanation
Step 1: Divisibility Conditions
15 se divide hone ke liye number ko 3 aur 5 dono se divide hona chahiye.
Digits given: {1,2,3,5}
Step 2: Condition for 5
Unit digit (D) hamesha 5 hona chahiye.
Step 3: Condition for 3
Sum of digits A+B+C+D must be divisible by 3.
A+B+C+5≡0(mod3)⟹A+B+C≡1(mod3)
Step 4: Possible Combinations for (A, B, C)
Niche diye gaye combinations ka sum (A+B+C) check karein:
| Digits Set |
Arrangements (p!n!) |
Count |
| {3,3,1} |
2!3! |
3 |
| {1,1,2} |
2!3! |
3 |
| {1,1,5} |
2!3! |
3 |
| {3,2,2} |
2!3! |
3 |
| {3,5,5} |
2!3! |
3 |
| {3,2,5} |
3! |
6 |
Step 5: Final Answer
Total Numbers=3+3+3+3+3+6