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JEE Advanced2022Paper 1MATH-I
Q.

The number of 4-digit integers in the closed interval formed by using the digits is ______.

Solution

Counting integers starting from 2

Case-I: If zero is on the 2nd place

i.e., $2\;0\;2\;\underbrace{\uparrow}_{5} \;\Rightarrow\; 5\text{ cases}$

or $2\;0\;\underbrace{\uparrow\;\uparrow}_{4,\;6} \;\Rightarrow\; 24\text{ cases}$

(Numbers except 0 or 2 in the 3rd place)

Case-II: If a non-zero number is on the 2nd place

i.e., $2\;\underbrace{\uparrow}_{5}\; \underbrace{\uparrow}_{6}\; \underbrace{\uparrow}_{6} \;=\;180\text{ cases}$


Counting integers starting from 3

$3\;\underbrace{\uparrow}_{6}\; \underbrace{\uparrow}_{6}\; \underbrace{\uparrow}_{6} \;=\;216\text{ cases}$


Counting integers starting from 4

Case-I: If 0, 2 or 3 is on the 2nd place

i.e., $4\;\underbrace{\uparrow}_{3}\; \underbrace{\uparrow}_{6}\; \underbrace{\uparrow}_{6} \;=\;108\text{ cases}$

Case-II: If 4 is on the 2nd place

i.e., $4\;4\; \underbrace{\uparrow}_{6}\; \underbrace{\uparrow}_{6} \;=\;36\text{ cases}$

Total

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