Can anyone help me with this?

Subhotosh Khan

Super Moderator
Staff member
Mr Whippy drove 120 km from Dublin to Newry. On the return trip, he drove 10 km/h slower than on the outward trip. If the return journey was 10 minutes longer, find his outward and inward speeds. I’ve tried so many different variations but none are correct. The answers are 90km/h and 80km/hView attachment 14040
Mr Whippy drove 120 km from Dublin to Newry. On the return trip, he drove 10 km/h slower than on the outward trip. If the return journey was 10 minutes longer, find his outward and inward speeds.

Let the

outward speed = O kmph

inward speed = I kmph = (O - 10) kmph

Time to travel outward = 120/O

Time to travel inward = 120/I = 120/(O-10)

Then we know: If the return journey was 10 minutes longer

120/(O-10) - 120/O = 1/6

Now solve for "O" from above and then solve for "I".

• Ialwaysneedhelp111

Ialwaysneedhelp111

New member
Mr Whippy drove 120 km from Dublin to Newry. On the return trip, he drove 10 km/h slower than on the outward trip. If the return journey was 10 minutes longer, find his outward and inward speeds.

Let the

outward speed = O kmph

inward speed = I kmph = (O - 10) kmph

Time to travel outward = 120/O

Time to travel inward = 120/I = 120/(O-10)

Then we know: If the return journey was 10 minutes longer

120/(O-10) - 120/O = 1/6

Now solve for "O" from above and then solve for "I".
Thank you so much

Ialwaysneedhelp111

New member
Mr Whippy drove 120 km from Dublin to Newry. On the return trip, he drove 10 km/h slower than on the outward trip. If the return journey was 10 minutes longer, find his outward and inward speeds.

Let the

outward speed = O kmph

inward speed = I kmph = (O - 10) kmph

Time to travel outward = 120/O

Time to travel inward = 120/I = 120/(O-10)

Then we know: If the return journey was 10 minutes longer

120/(O-10) - 120/O = 1/6

Now solve for "O" from above and then solve for "I".
I was just wondering. Why does this not work for distance / time ? Why do you have to do distance / speed ?

Jomo

Elite Member
I did not read the whole thread but I suspect that I can answer your question.

Let R = rate or speed, T = time and D = distance

RxT = D so D/T = R. Were you looking for rate? (If yes, then this is the correct formula)

RxT = D so D/R = T. Were you looking for times? (If yes, then this is the correct formula)

Another way to see this is to note the units for distance/time and distance/speed.

An example for distance/time could be for example 50 miles/2 hour which is a speed. So D/T = R
An example for distance/speed could be for 150 miles/(50 miles/hr) = 3 hours which is a time. So D/R=T