The average temperature for the first 9 days was 20 C and that of the first 5 was 25 C and that for the last 5 days was 15 C. What was the temperature on the fifth day?
- 25 C
- 20 C
- 30 C
- 15 C
- 27 C
The Usual Method
Total temperature for 9 days = 9 x 20 = 180 C
Total temperature for first 5 days = 5 x 25 = 125 C
Total temperature for last 5 days = 5 x 15 = 75 C
Also, total temperature for first 5 days = a + b
Where, a = total temperature for first 4 days and
b = temperature on the 5th day
Similarly, total temperature for last 5 days = b + c
Where, b = temperature on the 5th day and
c = total temperature for last 4 days
…… Eq. 1.
and …… Eq. 2.
Adding Eq. 1 and Eq. 2, we get: a + 2b + c = 200 C
Hence, temperature on 5th day = 20 C
Estimated Time to arrive at the answer = 45 seconds.
Since the average temperatures for the first 5 days and the last 5 days is ‘equidistant’ from the average temperature for the 9 days, we can simply take the arithmetic mean of 25 and 15 as 20 C as the temperature of the 5th day.
Estimated Time to arrive at the answer = 5 seconds.