In the 4-digit number X3Y7, (X and Y represents unknown digit)

1. What is the largest number?

2. What is the smallest number?

3. What number is closest to 3,590?

1. To make a largest number, replace both X and Y with the largest digit 9 , the result is 9,397;

2. Replace X with 1, which is the smallest digit possible for a 4-digit number; and replace Y with 0, the result is 1307;

3. Replace X with 3, and replace Y with 9. Thus, the number closest to 3590 is 3,397