Digits

How many natural numbers greater than 4000 are formed from the numbers 0,1,3,7,9 with the figures not repeated,

B) How many natural numbers will be less than 4000, and can the numbers be repeated?

Correct answer:

a =  144
b =  375

Step-by-step explanation:

$a=2\cdot 4\cdot 3\cdot 2+4\cdot 4\cdot 3\cdot 2\cdot 1=144$

$b=5+4\cdot 5+4\cdot 5\cdot 5+2\cdot 5\cdot 5\cdot 5=375$

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