Question

Bob drives 28 miles every half hour. If he drives 2 1/2 hours, how dar does he drive?

Answer 1

140 miles

1) Considering that Bob drives at a constant speed, we can write out:

hour mileage

1/2 28

2 1/2 x

2) Let's turn that Mixed Number into an improper fraction:

$2\frac{1}{2}=\frac{2\times2+1}{2}=\frac{5}{2}$

Note that we have kept the bottom number and then multiplied that by the whole number adding it to the numerator.

2.2) Now, We can write a pair of ratios rewriting 2 1/2 as 5/2 and then cross multiplying it:

$\begin{gathered} \frac{\frac{1}{2}}{\frac{5}{2}}=\frac{28}{x} \\ \frac{x}{2}=28\cdot\frac{5}{2} \\ \frac{x}{2}=\frac{140}{2}(\times2) \\ x=140 \end{gathered}$

3) Hence, the answer is Bob drives 140 miles in 2 1/2 hours