Ex.1.4 Q5 Integers Solution - NCERT Maths Class 7

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The temperature at \(12\) noon was \(10^\circ \rm{c}\)  above zero. If it decreases at the rate of \(2^\circ \rm{c}\) per hour until midnight, at what time would the temperature be \(8^\circ \rm{c}\) below zero? What would be the temperature at mid night?


 Video Solution
Ex 1.4 | Question 5

Text Solution


The temperature at \(12\) noon \(=10^\circ \rm{c}\) (given)

The temperature decreases \( 2^\circ \rm{c} = 1\) hour (given)

The temperature decreases \(1^\circ \rm{c} =\) \(1 \over 2\)hour

The temperature decreases \(18^\circ \rm{c}=\frac{1}{2} \times 18\)

(From \(10^\circ \rm{c}\) to \( 8^\circ \rm{c}\) below zero \(=9 \) hours)

Total time

\[\begin{align}&= 12\, \rm{noon}+9 \,\rm{hours}\\ &= 21 \,\rm{hours}\\&= 9\, \rm{pm}\end{align}\]

Thus, at \(9\) pm temperature would be \(8^\circ \rm{c}\) below zero.

ii) The temperature at \(12\) noon \(=10^\circ \rm{c}\)

The temperature decreases \(=2^\circ \rm{c}\) every hour

The temperature decreases in \(12\) hours \(=\;–2^\circ \rm{c} ×12 =24 ^\circ \rm{c}\) 

At midnight, the temperature will be \(=10^\circ \rm{c}+(–24)^\circ \rm{c} =–14^\circ \rm{c}\)

Therefore, the temperature at mid night will be \(14^\circ \rm{c}\) below \(0.\)

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