Question

It takes 3 hour 15 minutes to fly from city a to city b at constant speed. Find how long the journey takes if

A) the speed is 1×1÷2 times of the original speed and
B) if the speed is three-quarters of the original speed.

Answer 1

a) t= 2hours and 10 minutes

b) t=4hours and 20 minutes

v1t1=v2t2

Answer 2

Explanation:

rate = distance / time distance is constant (a-b) so call it D

time = distance / rate rate = speed (ie miles per hour = mph)

time = distance / speed

A) if the new speed is 1.5 of the original speed

original time = 3.25 hours or 195 minutes

3.25 = D / 1 new time = D/1.5 find new time

3.25 is to D as new time is to D/1.5

3.25/D = new time / D/1.5 multiple D/1.5 on both sides

(3.25/D) ( D/1.5) = new time the distance D cancels

3.25 (D / D) / 1.5 = new time

3.25 / 1.5 = 2.167 hours or 2 hours and 10 minutes

B) if the speed is 3/4 the original speed

original time = 3.25 hours or 195 minutes

3.25 = D / 1 new time = D/(3/4) find new time

3.25 is to D as new time is to D/0.75

3.25/D = new time / D/0.75 multiple D/0.75 on both sides

(3.25/D) ( D/0.75) = new time

3.25 (D / D) / 0.75 = new time

3.25 / 0.75 = 4.333 hours or 4 hours and 20 minutes