Lizzy: Ariella has $200 more in her son's saving account than Daniella has in her son's savings account. Ariella's account earns her simple interest at the rate of 10% per annum. If Daniella has $400, how much money will Arialla have after two years?.
Me: Hmmm, let me think. I think this is the detailed solution:
If Ariella has $200 more in her son's saving account than Daniella has, then she has $400 + $200 = $600. If she earns an interest of 10% in the first year, her savings account increases by 10 / 100 * $600 = $60. In the second year, she earns the same amount of interest, which $60 + $60 = $120. The total amount of money in Ariella's account after two years is $600 + $120 = $720. Final answer: 720.