walking 6 / 5 of his usual rate , a boy reaches his school 4 min early . find his usual time to reach the school ?
"speed ratio = 1 : 6 / 5 = 5 : 6 time ratio = 6 : 5 1 - - - - - - - - 6 4 - - - - - - - - - ? 24 m . answer : d"
multiply(4, 6)