Together, they can do
1
5

+
1
20
of the job in 1 minute

1
5

+
1
20

=
4
20

+
1
20

=
5
20

5
20

×
20
5

=
100
100
= 1

1
20

=
20
20
x

The friend can do
1
20


1
25
of the job in 1 day

The friend can do
5
100


4
100
of the job in 1 day

or
1
100

1
5

+
1
20
of the job in 1 minute

1
5

+
1
20

=
4
20

+
1
20

=
5
20

5
20

×
20
5

=
100
100
= 1

1
20

=
20
20
x

The friend can do
1
20


1
25
of the job in 1 day

5
100


4
100
of the job in 1 day

or
1
100

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Jan 13, 17 01:28 PM
What is the harmonic mean? How to calculate the harmonic mean?