Max runs the first 4km of her training session at 8 km/h. At least how many kilometers must she run at 15 km/h in order to average 12 km/h for the whole session.
Hello, begold91!
Max runs the first 4km of her training session at 8 km/h.
At least how many kilometers must she run at 15 km/h
in order to average 12 km/h for the whole session?
Max ran 4 km at 8 km/hr.
. . This took $\displaystyle \frac{4}{8} \,=\,\frac{1}{2}$ hours.
She will run $\displaystyle x$ more km at 15 km/hr.
. . This will take $\displaystyle \frac{x}{15}$ hours.
She will run a total of: $\displaystyle \frac{1}{2} + \frac{x}{15}$ hours.
She will run a total of $\displaystyle x + 4$ km at an average speed of 12 km/hr.
. . Her total time will be: $\displaystyle \frac{x+4}{12}$ hours.
There is our equation! . $\displaystyle \frac{1}{2} + \frac{x}{15}\:=\:\frac{x+4}{12}$