JEE Advance - Mathematics (2022 - Paper 1 Online - No. 7)
Explanation
This is a 4-digit integer whose 0th digit called D, 10th digit called C, 100th digit called B and 1000th digit called A.
Given range for possible number is 2022 to 4482.
So, position A can have digits 2, 3 or 4.
0, 6 and 7 can't put in A as number starts with 0, 6 or 7 don't fall in the range between 2022 to 4482.
So, Position A can be filled with 2, 3 or 4 in $${}^3{C_1} = 3$$ ways.
Position B can be filled by one of 0, 2, 3, 4, 6, 7
So, total possible ways for position B = $${}^6{C_1} = 6$$ ways
Similarly, Position C can be filled in $${}^6{C_1} = 6$$ ways
Position D can be filled in $${}^6{C_1} = 6$$ ways
$$\therefore$$ Total possible integer numbers starting with 2 or 3 or 4
$$ = 3 \times 6 \times 6 \times 6 = 3 \times 216 = 648$$
Now lets find those numbers which starts with 2 and 4 but don't fall in the range between 2022 to 4482.
Situation 1 :
$$\therefore$$ Total possible numbers starting with 200 are = 6
Situation 2 :
$$\therefore$$ Total possible number in this case = 1
Situation 3 :
$$\therefore$$ Total numbers in this case $$ = 2 \times 6 \times 6 = 72$$
$$\therefore$$ Total number that don't fall in the range 2022 to 4482 which starts with 2 or 4 are
$$= 6 + 1 + 72 = 79$$
$$\therefore$$ Total numbers falls in the range 2022 to 4482
$$=648-79$$
$$=569$$
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