Question

The mean temperature for the first 4 days in January was 1°C.

The mean temperature for the first 5 days in January was -1°C.
What was the temperature on the 5th day?

Answer 1

The temperature on the 5th day was of -9ºC.

Explanation:

Mean of a data-set

The mean of a data-set is the sum of all values in the data-set divided by the number of values.

The mean temperature for the first 4 days in January was 1°C.

This means that during the first 4 days, the sum of the temperatures was 4*1 = 4ºC.

The mean temperature for the first 5 days in January was -1°C.

First 4 days: Sum of 4º

5th day: Temperature of x.

The mean is -1, so:

`-1 = (4 + x)/(5)`

`x + 4 = -5`

`x = -9`

The temperature on the 5th day was of -9ºC.