Calculation:
According to the question;
The 4 digit number having 7 before 3 can be formed
Case I : When 7 is thousand placed, then 3 may be hundred place, tens place and unit place
From the following 73xy, 7x3y, 7xy3 are formed
Total such number formed = 3 × (8 × 7) = 168
Case II : When 7 is hundred placed, then 3 may be tens place and unit place
From the following x73y, x7y3 are formed
Total such number formed = 2 × (7 × 7) = 98
Case III : When 7 is tens place and 3 is unit place
From the following xy73 is formed
Total such number formed = 7 × 7 = 49
The total such number formed = 168 + 98 + 49 = 315
∴ The 4 digit number greater than 1000 with 7 before 3 is 315.
