Question

the temperature at 12 noon was 10 degree celcius above zero . if it decreases at the rate of 2 degrees celcius per hour until midnight , at what time would the temperature be 8 degree celius below zero ? what would be the temperature at midnight ?

Answer 1

At 12 noon, the temperature = 10° C above zero

The temperature is decreasing at 2° C per hour

8° C below zero = - 8° C

So, total fall in temperature from 10° C to 0° C and from 0° C to - 8° C = 18° C

Since the temperature falls 2° C in every one hour.
Therefore, to decrease 18° C, time taken = 18/2
= 9 hours

Present time is 12 noon so, the time when the temperature is - 8° C
= 12 noon + 9 hours
So, The time at which the temperature will be - 8° C = 9 PM
At 9 PM, the temperature is - 8° C, the temperature at 12 midnight will be =
(- 8° C) + (- 2° C × 3 hours)
= (- 8° C) + (- 6° C)
= - 14° C

So, at 12 midnight the temperature will be - 14° C.