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JEE Mains Model Paper 4
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© examsnet.com
Question : 4
Total: 90
In a certain city, all telephone numbers have six digits, the first two digits always being 41 or 42 or 46 or 62 or 64.How many telephone numbers have all six digits distinct?
840
8400
900
8000
Validate
Solution:
If first two digits is 41, the remaining 4 digits can be arranged in
8
C
4
= 8 × 7 × 6 × 5 = 1680 ways
Similar , If first two digits is 42,46,62,64, the remaining 4 digits can be arranged in
8
C
4
way i.e. 1680 ways
∴ Total numbers of telephone numbers having all six digits distinct = 5 x 1680 = 8400
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