Question

A car making a 111-km journey travels 41 km/h for the first 55.5 km. how fast must it go during the second 55.5 km to average 51 km/h?

Answer 1

over 55.5km v = 41km/h
start by solving total time (tt) = distance (d) / v, where d = vt
tt = 111km/51km/h = 2.18h
Now let's see it the first half in t plus the second half in t = 2.18h
t1 + t2 = 2.18h
(d1/v1) + (d2/v2) = 2.18h
(55/41) + (55/v2) = 2.18h
1.34h + 55/v2 = 2.18h
55/v2 = 2.18 - 1.34
55/v2 = 0.88
v2 = 55/0.88 = 62.5km/h