Question

The mean temperature for the first 4 days in January was 8°C.

The mean temperature for the first 5 days in January was 7°C.
What was the temperature on the 5th day?

Answer 1

3 °C

Explanation:

You want the temperature that, when added to four others, changes the mean from 8°C to 7°C.

Mean

The mean is the sum of the values in a data set, divided by the number of values. For the purpose here, we can assume that all of the first four temperatures were their mean. Then the mean after 5 days is ...

(8 +8 +8 +8 +x)/5 = 7

32 +x = 35 . . . . . . . . . . multiply by 5 and simplify

x = 3 . . . . . . . . . . . . subtract 32

The temperature on Jan 5 was 3°C.