Question:

The number of seven digits odd numbers, that can be formed using all the seven digits $1,2,2,2,3,3,5$ is_______

Updated On: Mar 20, 2025
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Correct Answer: 240

Approach Solution - 1

Digits are 1,2,2,2,3,3,5 
If unit digit 5 , then total numbers \(=\frac{6!}{3!2!}=60\)
If unit digit 3 , then total numbers \(=\frac{6!}{3!} =120\)
If unit digit 1 , then total numbers \(=\frac{6!}{3!2!}=60\)
∴ total numbers =60+60+120=240
So , the correct answer is 240

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Approach Solution -2

Digits are \( 1, 2, 2, 2, 3, 3, 5 \). If unit digit is 5, then total numbers are: \[ \frac{6!}{3!2!} = 60 \] If unit digit is 3, then total numbers are: \[ \frac{6!}{3!} = 120 \] If unit digit is 1, then total numbers are: \[ \frac{6!}{3!2!} = 60 \] Therefore, total numbers are: \[ 60 + 60 + 120 = 240 \]
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Concepts Used:

Complex Numbers and Quadratic Equations

Complex Number: Any number that is formed as a+ib is called a complex number. For example: 9+3i,7+8i are complex numbers. Here i = -1. With this we can say that i² = 1. So, for every equation which does not have a real solution we can use i = -1.

Quadratic equation: A polynomial that has two roots or is of the degree 2 is called a quadratic equation. The general form of a quadratic equation is y=ax²+bx+c. Here a≠0, b and c are the real numbers.