Chapter CSB, Problem 1.21E

To determine

To find:the time at which Marci drive an additional of 84 miles.

Answer to Problem 1.21E

  $t=4.77\text{hr}$ .

Explanation of Solution

Given:

Total distance covered by Marci is 238 miles at 3.5 hours.

Calculation:

As the distance covered is product of speed rate and time taken.

i.e. $dis=speed\times time$ .

therefore, the rate at which Marcicovered by 238 miles at 3.5 hours is

  $\begin{array}{l}\text{speed}=\frac{\text{distance}}{\text{time}}\left\{\text{speed-distance formula}\right\}\\ \text{speed}=\frac{\text{238}}{3.5}\{\text{substitutes these value}}\\ \therefore \text{speed}=\frac{\text{238}}{3.5}=68\text{miles/hr}\end{array}$

Now, to find the time at which Marci drive an additional of 84 miles:

Therefore, total distance covered is $238+87=325miles$

Therefore, total time taken is

  $\begin{array}{l}\text{time}=\frac{\text{distance}}{\text{speed}}\left\{\text{speed-distance formula}\right\}\\ \text{time}=\frac{325}{68}\{\text{substitutes these value}}\\ \therefore \text{time}=4.77\text{hr}\end{array}$

Hence, the time at which Marci drive an additional of 84 milesis $t=4.77\text{hr}$ .