Different introduction of LinearInterpolate

Hi all,
I’m a noob in UE4 and I found different expressions which confuse me like images below. Could anyone tell me which is right? Thanks a lot!

The text inside ue4 is right.
0 = b
1 = a

Thank you so much! Man

However dude, what I got is opposite to your answer.Seems text on official web is right…

confusion.jpg

So…
confused…
Right now…