Answer :

**Method 1: **

**Given:** Temperature at 12 noon = 10^{o}C

Change in temperature per hour = - 2^{o}C

**To Find: **Time at which temperature is 8ºC below zero = -8ºC.Temperature Difference = -8 - 10 = - 18ºC.

-2ºC change is in 1 hour

1ºC change will be in 1/2 hour.

18ºC change will be in 1/2 × 18 hours.

18ºC change will be in 9 hours.

So, the time at which the temperature is -8ºC = 12 noon + 9 hours = 9 p.m

Now, temperature at 12 midnight = 12 noon + 12 hours

Therefore, we need to find a change in temperature in 12 hours.

In 1-hour change is -2ºC, in 12 hours change will be 12 × -2ºC = -24ºC.

So, the temperature at midnight = 10ºC - 24ºC = - 14ºC

So, the temperature at midnight = 10ºC - 24ºC = - 14ºC

**Temperature at 12 noon = 10**

Method 2:

Given:

Method 2:

Given:

^{o}C

Change in temperature per hour = - 2^{o}C

**Therefore,**

Temperature at 1:00 PM = 10^{o}C + (-2^{o}C) = 8^{o}C

Temperature at 2:00 PM = 8^{o}C + (-2^{o}C) = 6^{o}C

Temperature at 3:00 PM = 6^{o}C + (-2^{o}C) = 4^{o}C

Temperature at 4:00 PM = 4^{o}C + (-2^{o}C) = 2^{o}C

Temperature at 5:00 PM = 2^{o}C + (-2^{o}C) = 0^{o}C

Temperature at 6:00 PM = 0^{o}C + (-2^{o}C) = - 2^{o}C

Temperature at 7:00 PM = - 2^{o}C + (-2^{o}C) = - 4^{o}C

Temperature at 8:00 PM = - 4^{o}C + (-2^{o}C) = - 6^{o}C

Temperature at 9:00 PM = - 6^{o}C + (-2^{o}C) = - 8^{o}C

Hence,

The temperature will be 8^{o}C below zero at 9:00 PM

Now,

Change in temperature in 12 hours = - 2^{o}C × 12

= - 24^{o}C

Also,

At midnight the temperature will be = 10 + (-24)

= - 14^{o}C

Hence,

**The temperature at midnight will be 14 ^{o}C below zero.**

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