Question 932174
1/a+1/b=1/x
1/30+1/60=1/x
60/1800+30/1800=1/x
90/1800=1/x
x=1800/90
x=20 hours working together
check
x/a+x/b=1
x/30+x/60=1
20/30+20/60=1
0.66666667+0.33333333=1
1=1
ok
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