if 10 typists can type 20 letters in 20 minutes , then how many letters will 40 typists working at the same rate complete in 1 hour ?
"no . of letters typing by 10 typists in 20 minutes = 20 no . of letters typing by 10 typists in 60 minutes = 20 * 3 = 60 no . of letters typing by 40 typists in 60 minutes = 60 / 10 * 40 = 240 answer : d"
multiply(divide(multiply(20, const_3), 10), 40)