Chapter SH, Problem 6.4MPS

a.

To determine

Tocalculate: average speed in miles per hour

Answer to Problem 6.4MPS

Speed $=12.0$ miles per hour

Explanation of Solution

Given information: Stefano Baldini won the 26.2-mile marathon in approximately 2 hours and 11 minutes

Formula used:Distance $=$ Speed $\times$ Time

Calculation:

Distance travelled by Stefano $=26.2$ miles

Time taken $=2$ hours 11 minutes

As 1 minute $=\frac{1}{60}$ hour,

2 hours 11 minutes $=2+\frac{11}{60}=\frac{120+11}{60}=\frac{131}{60}$ hours

So,

Time taken $=\frac{131}{60}$ hours

So,

  $Speed=\frac{Distance}{Time}=\frac{26.2}{\frac{131}{60}}=12$ miles per hour

Now round off speed to the nearest tenth.

Speed $=12.0$ miles per hour

b.

To determine

To calculate: average speed in kilometres per hour

Answer to Problem 6.4MPS

Speed $=19.3$ kilometres per hour

Explanation of Solution

Calculation:

Distance travelled by Stefano $=26.2$ miles

As 1 mile = 1.61 kilometres,

Distance travelled (in miles) $=26.2\times 1.61=42.182$ kilometres

Time taken $=2$ hours 11 minutes

As 1 minute $=\frac{1}{60}$ hour,

2 hours 11 minutes $=2+\frac{11}{60}=\frac{120+11}{60}=\frac{131}{60}$ hours

So,

Time taken $=\frac{131}{60}$ hours

So,

  $Speed=\frac{Distance}{Time}=\frac{42.182}{\frac{131}{60}}=19.32$ kilometres per hour

Nowround off the speed to the nearest tenth.

Speed $=19.3$ kilometres per hour