are three. ypist in can type an average of 6 letters arrive for being of the rate of 15 leters Per hows. fraction of 81 There Typist houx ay what busy? by what is the average waiting to be Red Cywhat is the to Spend including mote average bote waiting dy what is the probabiliy the the an office sach letters Pet time call the typist will be 20 min ge number ty Peat at of typing time of a letters time a letter has and fot being by Red that waiting time.​