In which situation would a savings account be the best investment to earn interest? saving for retirement in 20 years saving to buy a new car in three years saving to buy a new house in seven years saving to easily access the money when needed

Assuming that the interest rate in each case is the same, the only factors that come into play are the length of time, and the accessibility of the money. The longer the money is left alone, the more money it will accrue, meaning the first option "saving for retirement in 20 years" is the best option. The two below it are a shorter length of time and will therefore accrue less, and the final option is less profitable because withdrawing from the account would decrease the total interest earned.