How many numbers between 100 and 1000 have the digit 7 exactly once?

How many numbers between 100 and 1000 have 4 in the unit place?

Find the sum of all natural numbers between 100 and 1000 which are multiples of 7 .

How many numbers can be made with the digits 3, 4, 5, 6, 7, 8 lying between 3000 and 4000 which are divisible by 5 while repetition of any digit is not allowed in any number

How many 10-digit numbers can be written by using the digits 1 and 2?

How many numbers greater than 24000 can be formed by using digits 1, 2, 3, 4, 5 when no digit is repeated?