Quantitative Aptitude – How many 4-digit numbers, each greater than 1000


Slot – 1 – Quantitative Aptitude – How many 4-digit numbers, each greater than 1000


Q. How many 4-digit numbers, each greater than 1000 and each having all four digits distinct, are there with 7 coming before 3?
Answer: 315

Solutions:
From the given condition the four digit number can be of the form
Case 1) 73ab , 7a3b, 7ab3 – : Total such numbers = 3*(8*7) = 168
Case 2) a73b , a7b3 – : Total such numbers = 2*(7*7) = 98
Case 3) ab73 -: Total such numbers = 7*7 = 49
Thus total such four digit numbers = 168+98+49 =315


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