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Position of a number when numbers formed from given digits are listed in order

This type of question, asked 2 times: 29 Jan 2023, 31 Jan 2023. All 3 questions below, oldest first.

Try each one first, then open its answer.

  1. Question 1

    29 Jan 2023

    90
    If all the six digit numbers x1x2x3x4x5x6x_{1}x_{2}x_{3}x_{4}x_{5}x_{6} with 0<x1<x2<x3<x4<x5<x60 <x_{1}<x_{2}<x_{3}<x_{4}<x_{5}<x_{6} are arranged in the increasing order, then the sum of the digits in the 72th 72^{\text{th~}} number is

  2. Question 2

    29 Jan 2023

    89
    Five-digit numbers are formed using the digits 1, 2, 3,5, 7 with repetitions and are written in descending order with serial numbers. For example, the number 77777 has serial number 1 . Then the serial number of 35337 is

  3. Question 3

    31 Jan 2023

    86
    Let 5-digit numbers be constructed using the digits 0,2,3,4,7,90,2,3,4,7,9 with repetition allowed, and are arranged in ascending order with serial numbers. Then the serial number of the number 42923 is