For how many numbers from 5000 to 7999 do the digits add up to an odd number?

i. For how many numbers from 5000 to 7999 do the digits add up to an odd number? Hint. Use a one-to-one map, follow these steps: 1. define the set A of numbers with desired property in given range, and the set with the others 2. describe a one-to-one map (pairing) that associates every element in A with a unique element in A and viceversa 3. conclude that the two sets have the same size, and calculate the size of A i. For how many numbers from 5000 to 7999 do the digits add up to an odd number? Hint. Use a one-to-one map, follow these steps: 1. define the set A of numbers with desired property in given range, and the set with the others 2. describe a one-to-one map (pairing) that associates every element in A with a unique element in A and viceversa 3. conclude that the two sets have the same size, and calculate the size of A