Question 35
Bruno has a list of all the 10-digit natural numbers that can be formed using only digits 1, 2, 3 and 4 and in addition to having an equal number of digits 1 and 2, for example, 3333333333, 1111342222 etc. Bernardo has the list of all the 20-digit natural numbers formed by 10 digits 1 and 10 digits 2. Show that Bruno's list has the same number of digits as Bernardo's list.