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Permutations and Combinations question

2002 · Shift 0 · Q109
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Permutations and Combinations question

2002 · Shift 0 · Q109

JEE MainMathematicsPermutations and CombinationsMCQ+4 / −1
Five digit number divisible by 3 is formed using 0, 1, 2, 3, 4 and 5 without repetition. Total number of such numbers are :
  1. A
    312
  2. B
    3125
  3. C
    120
  4. D
    216
View written solutionFree

Correct answer: D

  1. Condition for divisibility by 3

A number is divisible by 333 if the sum of its digits is divisible by 333.

We must form a 5-digit number using digits from {0,1,2,3,4,5}\{0,1,2,3,4,5\}{0,1,2,3,4,5} without repetition.

So we choose any 5 digits out of these 6.

The sum of all six digits is 0+1+2+3+4+5=150+1+2+3+4+5=150+1+2+3+4+5=15 which is divisible by 333.

If one digit ddd is omitted, then the sum of the chosen 5 digits is 15−d15-d15−d For divisibility by 333: 15−d≡0(mod3)15-d \equiv 0 \pmod{3}15−d≡0(mod3) Since 15≡0(mod3)15 \equiv 0 \pmod{3}15≡0(mod3), we need d≡0(mod3)d \equiv 0 \pmod{3}d≡0(mod3) So the omitted digit must be one of 0,30,30,3.

Thus there are only 2 valid sets of 5 digits:

  • omit 000: digits {1,2,3,4,5}\{1,2,3,4,5\}{1,2,3,4,5}
  • omit 333: digits {0,1,2,4,5}\{0,1,2,4,5\}{0,1,2,4,5}

  1. Count numbers for each valid set

Case 1: Omit 000

Digits are {1,2,3,4,5}\{1,2,3,4,5\}{1,2,3,4,5}.

All 5 digits are nonzero, so every permutation gives a valid 5-digit number.

Number of such numbers: 5!=1205! = 1205!=120

Case 2: Omit 333

Digits are {0,1,2,4,5}\{0,1,2,4,5\}{0,1,2,4,5}.

Total permutations of these 5 digits: 5!=1205! = 1205!=120

But those starting with 000 are not 5-digit numbers. Fix 000 in the first place, and arrange the remaining 4 digits: 4!=244! = 244!=24

So valid 5-digit numbers in this case: 120−24=96120-24=96120−24=96


  1. Total count

Therefore, total numbers divisible by 333 are 120+96=216120+96=216120+96=216


  1. Option check

The correct option is: 216\boxed{216}216​ So Option D is correct.

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