a) 320
b) 360
c) 540
d) 720
Answer: c
Explanation: As per the given condition, number in the highest position should be either 6 or 7, which can be done in 2 ways.
If the first digit is 6, the other digits can be arranged in $$\frac{{6!}}{{2!}}$$ = 360 ways.
If the first digit is 7, the other digits can be arranged in $$\frac{{6!}}{{2! \times 2!}}$$ = 180 ways.
Thus required possibilities for n,
= 360 + 180
= 540 ways
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