Janice can type in 30 min Bianca can type in 45 min how long if they work together
J speed is one thing/30 min
B speed is one thing/45 min
total speed is 1thing/30min + 1thing/45 min
= (1/30+1/40) things/min
= 7/120 things/min
or
120/7 minutes/thing :)
120/7 = about 17.1 minutes