if 20 typists can type 50 letters in 30 minutes , then how many letters will 40 typists working at the same rate complete in 1 hour ?
"no . of letters typing by 20 typists in 30 minutes = 50 no . of letters typing by 20 typists in 60 minutes = 50 * 2 = 100 no . of letters typing by 40 typists in 60 minutes = 100 / 10 * 40 = 400 answer : a"
multiply(divide(multiply(const_60.0, const_3), 20), 40)