Question

The temperature at$9a.m$. was $20°C$ above zero. If it decreases at the rate of $3°C$ per hour until $9p.m$., at what time would the temperature be $10°C$ below zero? What would be the temperature at $9p.m.$

Answer 1

Given us, The temperature at$9a.m$. was $20°C$ above zero

And also it decreases at the rate of $3°C$ per hour until $9p.m$

This total of 12 hrs

So, the Temperature at $9p.m.$= $20°C-12\times 3°C=20°C-36°C=-16°C$ below zero.

Also the time at which the temperature will be $10°C$ below zero suppose it be $x$

Now,

$$\begin{gathered} 20°\mathrm{C}-3\times \mathrm{x}=-10°\mathrm{C} \\ \Rightarrow 3\mathrm{x}=-20-10 \\ \Rightarrow 3\mathrm{x}=-30 \\ \Rightarrow \mathrm{x}=-10 \\ \mathrm{i}.\mathrm{e}10\mathrm{hrs}\mathrm{after}\mathrm{temperature}\mathrm{will}\mathrm{be}10°\mathrm{C}\mathrm{below}\mathrm{zero} \end{gathered}$$

At time $7PM$ the temperature be $10°C$ below zero