Question 397946
it takes mang kaloy 3 hrs to plow his ricefield with his new tractor.
 using the old tractor it takes him 5 hrs.
 if his son helped him plow the ricefield how long will it take them to plow the ricefield using both tractors
:
Let t = time required working together
Let the completed job = 1 (a plowed rice field)
:
{{{t/5}}} + {{{t/3}}} = 1
multiply thru by 15, results
3t + 5t = 15
8t = 15
t = {{{15/8}}}
t = 1.875 hrs, or 1 + .875(60) = 1 hr 52.5 min