Question 93396
ran the first 350m of the race at 25.2km/h.then setting into a steady 18km/h he ran the next 1000m.he made a dash for it toward the finishing line,running the last150m at 27km/h.how much time did he take to finish the race and what was his average speed.
 
Find the time of each of the 3 stages: Time = dist/speed

Change meters to km, divide by 1000 and you have
Stage 1 + Stage 2 + Stage 3
{{{.350/25.2}}} + {{{1.000/18}}} + {{{.150/27}}}
:
The common denominator: 25.2*18*27 = 12700.8
{{{(486(.350) + 680.4(1.000) + 453.6(.150))/12700.8}}} = {{{(170.1 + 680.4 + 68.04)/12700.8}}} = {{{(918.54)/12700.8}}} = .072321 hr 
:
.072321 & 60 = 4.34 min or about 4 min 20.4 sec
:
Average speed, (speed = dist/time):
{{{(.350 + 1.000 + .150)/.72321}}} = {{{1.500/.072321)}}} = 20.74 km/hr