mary invested a certain sum of money in a bank that paid simple interest . the amount grew to $ 260 at the end of 2 years . she waited for another 4 years and got a final amount of $ 380 . what was the principal amount that she invested at the beginning ?
"what shall be the rate of interest . ? does that is not required for the calculation ? not really ! keep in mind that the interest earned each year will be the same in simple interest . at the end of 2 years , amount = $ 260 at the end of 6 years , amount = $ 380 this means she earned an interest of $ 120 in 4 years . or $ 30 in each year . we know that the interest earned each year will be the same . therefore she must have earned $ 60 in 2 years . hence principal amount = $ 260 - $ 60 = $ 200 option a"
subtract(260, multiply(divide(subtract(380, 260), 4), 2))