Question

Sam left for school at 8:00, walking at a speed of 2 mph. Soon after, his father discovered that Sam left behind his project that was due that same day. Sam's father left home 20 minutes after Sam, and his average (he was driving) was 12mph. At what time will Sam's father give the project to Sam?

Answer 1

We use the formula d = rt  where d = distance, r = rate, t = time

Equation for Sam:
$d=( r_{1})(t)$
$d = 2t$

Equation for Sam's father:
$d = (r_{2})(t - 0.33)$
d = (12)(t - 0.33)
d = 12t - 4

Since Sam and his father have the same distance from their home to Sam's school, then
2t = 12t - 4
4 = 12t - 2t
4 = 10t
4/10 = t
t = 0.4 hrs or 24 mins

Sam travel 24 mins from home to school and his father travel 4 mins from home to school. Therefore, it was about 8:24 when Sam's father give the project to Sam.