їде vs. іде vs. йде

[anderswilder]

On the exercises about verbs of motion, it seems these three spellings are all accepted. Can someone please explain the difference(s) between them to me?
Are all three commonly used interchangeably, or is there a rule about when to use each spelling, or this a simple mistake?

Thanks!
Anders

[greg.mort]

Їде is from the verb їхати (to ride, usually implying some form of transportation).

Вона їде на мотоциклі - She is riding the motorcycle

Йде, іде is from the verb йти (to go, to walk, implying walking by foot, it has myriad additional uses which I believe this course is not touching at this point)
і will replace й if a preceding word ends in constant.

Вона йде в парк.
Він іде в парк - she/he is going (walking) to the park

Hope this gives you an idea.

[mizail]

We use їде when talk about a vheicle: a car, a bus, a motorcycle, a bicycle, a train and other. We use іде = йде when talk about walking (something that have legs): a human,an animal, a robot ... For exemple, a robot with the legs - iде, a robot with the wheels - їде :)

A bird iде (with the legs) on the ground, but летить (with the wings) in the sky.

іде = йде = to move with the legs = walk. About i/й read here: https://www.duolingo.com/comment/9012790

[basmur]

Іде = йде (ideh = ydeh). We write іде after the consonant and йде after the vowel.

Moves on wheels = їде (yeedeh).
Moves in the liquid environment = пливе (pliveh).
Moves in the gas environment = летить (letit').