1.1. Vasya thought of a natural number greater than 99 but less than 1000. The sum of the first and last digits of this number is 1, and the product of the first and second digits is 4. What number did Vasya think of?
Answer: 140

Solution. Note that the sum of 1 can only be obtained by adding the digits 1 and 0, and the first digit of the number cannot be 0, so it is 1, from which the last digit is 0. Since the product of the first and second digits is 4, we get that the second digit is 4, and the answer is the number 140.