Question

The mean temperature for the first 4 days in January was 7°C. The mean temperature for the first 5 days in January was 9°C. What was the temperature on the 5th day?

Answer 1

11 C

Explanation:

To find the mean (average), you have to add all and divide by 2, so if you reverse this, you get (7 + X)/2 = 9 , 9 * 2 - 7 = 11

Answer 2

If the mean was 7 for the first 4 days that means the sum of temperatures of the first 4 days was 7 * 4 = 28. Similarly, the sum of temperatures of the first 5 days was 9 * 5 = 45 so that means that the temp. on the 5th day was 45 - 28 = 17°C.