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Permutations and Combinations question

2021 · 18 Mar · Shift 1 · Q38
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  5. /2021 · 18 Mar · Shift 1 · Q38

Permutations and Combinations question

2021 · 18 Mar · Shift 1 · Q38

JEE MainMathematicsPermutations and CombinationsMCQ+4 / −1
The sum of all the 4-digit distinct numbers that can be formed with the digits 1, 2, 2 and 3 is :
  1. A
    26664
  2. B
    122664
  3. C
    122234
  4. D
    22264
View written solutionFree

Correct answer: A

  1. Form all distinct 4-digit numbers using digits 1,2,2,31,2,2,31,2,2,3

Since the digit 222 is repeated twice, the number of distinct 4-digit numbers is 4!2!=12.\frac{4!}{2!}=12.2!4!​=12.

  1. Use place value symmetry

In all distinct arrangements of the multiset {1,2,2,3}\{1,2,2,3\}{1,2,2,3}, each position (thousands, hundreds, tens, units) gets each digit equally often, accounting for repetition properly.

Let us count how many times each digit appears in a fixed position.

  • Total distinct numbers =12=12=12
  • Total number of positions filled across all numbers =12×4=48=12\times 4=48=12×4=48

Now:

  • Digit 111 appears once in each number, so across all numbers it appears 121212 times total.
  • Digit 333 appears once in each number, so across all numbers it appears 121212 times total.
  • Digit 222 appears twice in each number, so across all numbers it appears 242424 times total.

By symmetry, these appearances are equally distributed among the 4 places:

  • 111 appears 12/4=312/4=312/4=3 times in each place.
  • 333 appears 12/4=312/4=312/4=3 times in each place.
  • 222 appears 24/4=624/4=624/4=6 times in each place.

So the sum of digits appearing in any one place is 1⋅3+2⋅6+3⋅3=3+12+9=24.1\cdot 3 + 2\cdot 6 + 3\cdot 3 = 3+12+9=24.1⋅3+2⋅6+3⋅3=3+12+9=24.

  1. Compute total sum

Each place contributes:

  • thousands place: 24×100024\times 100024×1000
  • hundreds place: 24×10024\times 10024×100
  • tens place: 24×1024\times 1024×10
  • units place: 24×124\times 124×1

Hence total sum is 24(1000+100+10+1)=24×1111=26664.24(1000+100+10+1)=24\times 1111=26664.24(1000+100+10+1)=24×1111=26664.

  1. Check options

266642666426664 matches Option A.

Therefore, the required sum is 26664.\boxed{26664}.26664​.

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