What Minecraft parkour jump is possible but hard?

I'm making a custom Minecraft parkour map but I'm not sure whether the jumps are possible or not. I can't really test them because I'm horrible at parkour, so it wouldn't really work out. If I place a block down, then have a 4 block gap in between another block that is 1 block higher than the original block, is that a possible jump? Also, what is the hardest possible jump?

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