Question

The temperature at 12 noon at a certain place was 18° above zero. If it decreases at the rate of 3° per hour at what time if would be 12° below zero?

(i) 12 mid night 

(ii) 12 noon 

(iii) 10 am 

(iv) 10 pm

Answer 1

(iv) 10 pm  

’Temperature at 12 noon = 18° above zero = +18° 

Rate of decrease per hour = -3° 

Temperature 12° below zero = -12° 

-12 is 30 units to the left of +18° 

Time at which it reach -12° = \(\frac{30}{3}\) = 10 h 

10 hrs after 12 noon = 10 pm