walking with 4 / 5 of my usual speed , i miss the bus by 4 minutes . what is my usual time ?
"speed ratio = 1 : 4 / 5 = 5 : 4 time ratio = 4 : 5 1 - - - - - - - - 4 4 - - - - - - - - - ? è 16 answer : a"
multiply(divide(4, divide(5, 4)), 5)