Question

The temperature recorded at 12 noon was 15 degrees celsius above 0. it decreases at the rate of 3 degree Celsius per hour until midnight ,at what time would the temperature be 9 degree Celsius below zero. What t would be the temperature at midnight?

Answer 1

At 12 noon, the temperature = 15° C above zero

The temperature is decreasing at 3° C per hour

9° C below zero = - 9° C

So, total fall in temperature from 15° C to 0° C and from 0° C to - 9° C = 24° C

Since the temperature falls 3° C in every one hour.
Therefore, to decrease 24° C, time taken = 24/3
= 8 hours

Present time is 12 noon so, the time when the temperature is - 9° C
= 12 noon + 8 hours
So, The time at which the temperature will be - 9° C = 8 PM
At 8 PM, the temperature is - 9° C, the temperature at 12 midnight will be =
(- 9° C) + (- 3° C × 4 hours)
= (- 9° C) + (- 12° C)
= - 21° C

So, at 12 midnight the temperature will be - 21° C.