Math, asked by shambhavirai, 1 year ago

Five digit number divisible by 3 is formed using 0,1,2,3,4,6 and 7 without repetition. Total number of such numbers are?:
(1)312
(2)3125
(3)120
(4)216

My answer is coming out to be 504. I don't know where I am going wrong.
Please help


poorvitha1231: i think its based on permutations chapter
poorvitha1231: is it
shambhavirai: Yes it is
raven01: i think something is wrong in this question
raven01: a number divisible by 3 or 5 which is in the question
raven01: plz check the question again and tell me
shambhavirai: number divisible by 3

Answers

Answered by sunnygopid
6
Five digit number divisible by 3 is formed using 0,1,2,3,4,6 and 7 without repetition. Total number of such numbers are?: 

ans is 216


shambhavirai: How?
sunnygopid: We choose the most restrictive digit first, which is the
first digit. It can be chosen 4 ways, so

choose the first digit 4 ways. (It CANNOT be 0)
Choose the second digit 4 ways. (It CAN be 0)
Choose the third digit 3 ways.
Choose the fourth digit 2 ways.
Choose the fifth digit 1 way.

4×4×3×2×1 = 4×4! = 96

Answer: 120+96 = 216
shambhavirai: why 4 ways for the first digit ???? And the rest also..????
sunnygopid: We choose the most restrictive digit first, which is the
first digit. It can be chosen 4 ways, so

choose the first digit 4 ways.
shambhavirai: Why 4 and not 6???
shambhavirai: I am sorry but I am just s confused
sunnygopid: No other choice of 5 digits can have a sum divisible
by 3, because there is no other way to make the
sum 12 or 15, and we certainly can't have a sum of
9 or 18.
sunnygopid: in other cases your ans is also correct
shambhavirai: Ok thanks
Answered by amitnrw
3

600 Five digit number divisible by 3 can be formed using 0,1,2,3,4,6 and 7 without repetition

Step-by-step explanation:

Five digit number divisible by 3 is formed using 0,1,2,3,4,6 and 7 without repetition.

5 numbers out of 7 can be selected in ⁷C₅  = 21 ways

But out of 21 ways

as sum of all 7bdigits = 0+ 1+ 2 + 3 + 4 + 6 + 7 = 23

We need 5 digits  hence we need to leave 2 Digit with sum  = 2 , 5 , 8 , 11 to have remaining 5 Digits  with sum divisible by 3

0 + 2 = 2  ,   1 + 4 = 2 + 3 = 5    ,  1+7 = 2 + 6  = 8  ,  4 + 7 = 11

Sum is divisible by 3  in below cases only

01236 - Numbers can be formed = 4 * 4! = 96

04236 - Numbers can be formed = 4 * 4! = 96

07236 - Numbers can be formed = 4 * 4! = 96

01347 - Numbers can be formed = 4 * 4! = 96

01467 - Numbers can be formed = 4 * 4! = 96

13467 -  Numbers can be formed = 5!  = 120

Total Number = 96 + 96 + 96 + 96 + 96  + 120 = 600

Learn more:

A two digit number is formed with digits 2, 3, 5, 7, 9 without repetition ...

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