Question 908158
a=1 b=1 c=0.75
1/a+1/b+1/c=1/x
1/1+1/1+1/0.75=1/x
0.75/0.75+0.75/0.75+1.0/0.75=1/x
2.5/0.75=1/x
x=0.75/2.5
x=.3 hours working together
.3 hours is 3/10*60=18 minutes
check
1/a+1/b+1/c=1/x
1/1+1/1+1/0.75=1/0.3
0.75/0.75+0.75/0.75+1.0/0.75=1/0.3
2.5/0.75=1/0.3
0.75/2.5=0.3
0.3=0.3
ok
18/60+18/60+18/45=1
54/180+54/180 +72/180=1
180/180=1