求教几道prep的题

kittenalways

if each term in the sum a1+a2+...+an is either 7 or 77 and the sum equals 350. n=？  40

a committee of 3 people is to be chosen from 4 married couples. what's the number of differnt committees that can be choosen if 2 people who are married to each other cannot both serve on the committee?  32

a certain city with a population of 132000 is to be divided into 11 voting districts, andno district is to have a population that is more than 10% greater than the population of any other district. minimum possible population that the least population district =?  11000