Question 917496
1/a+1/b=1/x
1/3+1/-9=1/x
-9/-27+3/-27=1/x
-6/-27=1/x
x=-27/-6
x=4.5 hours working together
Add 4:30 to 9:30
 4:30 
+9:30
13:60
14:00=2 pm
check
x/a+x/b=1
x/3+x/-9=1
4.5/3+4.5/-9=1
1.5+-0.5=1
1.0=1
ok
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