Ex.1.4 Q5 Integers Solution - NCERT Maths Class 7

Go back to  'Ex.1.4'

Question

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?

 

Text Solution

Steps:

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 \(0.\)

  
Learn from the best math teachers and top your exams

  • Live one on one classroom and doubt clearing
  • Practice worksheets in and after class for conceptual clarity
  • Personalized curriculum to keep up with school