# Harmonic Mean

Today we will learn **Harmonic Mean Formula With Example**. It is the total number of items of a value divided by the sum of reciprocal of values of variables. It is specified average which solves problems involving variables expressed in within ‘Time rates’ that vary according to time.

If x_{1}, x_{2}, …, x_{n} are ‘n’ values for discrete series without frequency, then their Harmonic Mean (HM) is,

**Note:** For better understanding I suggest you to check my post on **Arithmetic Mean Formula With Example and Geometric Mean Formula With Example **.

### Individual Series

\[HM=\frac{n}{\sum{\frac{1}{{{x}_{i}}}}}\]

### Discrete Series

\[HM=\frac{n}{\sum{{{f}_{i}}(\frac{1}{{{x}_{i}}})}}\]

### Continuous Series

\[HM=\frac{n}{\sum{{{f}_{i}}(\frac{1}{{{m}_{i}}})}}\]

m_{i} = Mid value of each class interval.

## Weighted Harmonic Mean

\[{{H}_{W}}=\frac{\sum{{{W}_{i}}}}{\sum{{{W}_{i}}(\frac{1}{{{x}_{i}}})}}=\frac{\sum{W{{x}_{i}}}}{\sum{{{W}_{i}}}}\]

Example 01 |

**The daily incomes of 5 families in a very rural village are given below. Compute HM.**

Family | 1 | 2 | 3 | 4 | 5 |

Income($) | 85 | 90 | 70 | 50 | 60 |

**Solution:**

Family | Income (x) | Reciprocal (1/x) |

1 | 85 | 0.0117 |

2 | 90 | 0.0111 |

3 | 70 | 0.0143 |

4 | 50 | 0.02 |

5 | 60 | 0.0167 |

∑ (1/x) = 0.0738 |

\[HM=\frac{n}{\sum{\frac{1}{{{x}_{i}}}}}=\frac{5}{0.0738}=67.75\]

Example 02 |

**A man travel by a car for 3 days he covered 480 km each day. On the first day he drives for 10 hrs at the rate of 48 KMPH, on the second day for 12 hrs at the rate of 40 KMPH, and the third day for 15 hrs at the rate of 32 KMPH. Compute HM and weighted mean and compare them.**

**Solution:**

x | 1/x |

48 | 0.02083 |

40 | 0.025 |

32 | 0.03125 |

∑ (1/x) = 0.07708 |

\[HM=\frac{n}{\sum{\frac{1}{{{x}_{i}}}}}=\frac{3}{0.07708}=38.92\]

Now, we will calculate weighted Mean,

W | x | Wx |

10 | 48 | 480 |

12 | 40 | 480 |

15 | 32 | 480 |

∑ W = 37 | ∑ Wx = 1440 |

\[{{H}_{W}}=\frac{\sum{W{{x}_{i}}}}{\sum{{{W}_{i}}}}=\frac{1440}{37}=38.92\]

Example 03 |

**Find the HM of the following data.**

Class | 0-10 | 10-20 | 20-30 | 30-40 | 40-50 |

Frequency | 5 | 15 | 25 | 8 | 7 |

**Solution:**

Class Interval | Frequency (f) | Mid-value (m) | Reciprocal (1/m) | f(1/m) |

0-10 | 5 | 5 | 0.2 | 1 |

10-20 | 15 | 15 | 0.0666 | 0.999 |

20-30 | 25 | 25 | 0.04 | 1 |

30-40 | 8 | 35 | 0.0285 | 0.228 |

40-50 | 7 | 45 | 0.0222 | 0.1554 |

∑ f = 60 | ∑ f(1/m) = 3.3824 |

\[HM=\frac{n}{\sum{{{f}_{i}}(\frac{1}{{{m}_{i}}})}}=\frac{60}{3.3824}=17.74\]

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