Answer:
120 hours
Step-by-step explanation:
Both take 30 minutes, meaning that in one minute they do 1/ 30 of the task
if Gertrude takes forty minutes then in one minute she does 1/40 of the task
To get the fraction that Bertha does in one hour we subtract the fraction that Gertrude does from the fraction they both do in one minute.
1/30-1/40=1/120
thus the number of hours taken is given by taking the reciprocal of 1/120
=120 hours
