Question 909184
1/a+1/b=1/x
1/4+1/5=1/x
5/20+4/20=1/x
9/20=1/x
x=20/9 hours working together
x=2.22222222 hours working together
check
x/a+x/b=1
(20/9)/4+(20/9)/5=1
5/9+4/9=1
1.0=1
ok