Question 1173899
The work rate of technician 1, r1 = 1 alarm/12 hr = 1/12 (alarm/hr)
The work rate of technician 2, r2 = 1/10 = 1/10 (alarm/hr)
If technician 1 works 6 hr, he will complete 1/12*6 = 1/2 of the alarm
So technician 2 will take (1/2)/(1/10) = 5 hrs to complete the alarm wiring