Two features (a Champion Fighter's level 7 Remarkable Athlete, and a Thief Rogue's level 3 Second Story Work) give a modifier to long jump distance.
Three features (the Jump spell, the Boots of Striding and Springing and a Monk's level 2 Step of the Wind) give a multiplier to jump distance.
If a character is under the effect of both a jump modifier and a jump multiplier, how is the calculation done ?
For example, if a Champion with a Strength of 20 and under the effect of a Jump spell makes a running long jump, would his total long jump distance be :
1) 65 feet [ (20 x 3) + 5 ]
2) 75 feet [ (20 + 5) x 3 ]
Best Answer
There are no rules but 65 feet makes the most sense
Jump
Remarkable Athlete
Chronological order
The bonus to jump should follow the order in which the bonuses are actually applied in the game. In other words, since you apply the spell before you jump, your jumping distance is tripled first. Then, when you actually do a running long jump, the remarkable athlete bonus gets added onto that.
Thus, the math follows the order in which the bonuses are actually applied.
Constant versus situational bonus
Another way to reach the same conclusion is to think of the two effects in terms of how general they are. While under the effects of jump, your jump distance is constantly tripled. However, remarkable athlete only gives you the bonus to jump when you are actually making a running long jump. If you make a standing long jump you don't get any bonus at all from remarkable athlete, but jump still applies.
I would argue the constant general effect gets applied, and then the situational bonus gets added on top of that.
Either way you think about it, the math would work out to: (20 x 3) + 5 = 65 feet
Note regarding jumping and speed
The distance you jump is indeed limited by your speed but with dashing and other means of speed increases the jump distances can be kept relevant as indicated in this conversation with Jeremy Crawford:
This is discussed more here Does a ring of jumping let you jump farther than your normal movement? and What happens when you run out of movement while jumping?