Question 35286
The formula for this kind of problem is
t/A + t/B = 1
where t is the time worked together and A and B are the individual times...so for this problem, we have (in minutes)
t/70 + t/150 = 1
multiply everything by 1050 to clear fractions, then solve and get
15t + 7t = 1050
22t = 1050
t = 525/11 minutes together or in hours that would be
t = 525/660 = 35/44 hours
and thus their work rate is the inverse of this, meaning they work at 
44/35 jobs per hour.