The world of sports is one of the only places where addition by subtraction is a real thing.

In many locker rooms, chemistry outweighs arithmetic, and the makeup of a team can be just as important as the talent on hand.

In Texas A&M’s case, though, subtraction has been just that: subtraction. Just as everyone expected before the season, Kevin Sumlin’s offense has been far less potent without former Heisman winner Johnny Manziel holding the wheel.

That should come as no surprise, but less than two months ago folks were wondering if life in Aggieland would be even better without Johnny Football. Watching Kenny Hill throw for approximately 2,253 yards and 24 touchdowns in the opener against South Carolina had fans seeing through maroon-colored glasses.

A&M has fallen back to earth, though, and it has to do in part with an offense that’s not up to par without Manziel in College Station.

For a quick refresher on the basic tenets of Sumlin’s Air Raid passing attack: the Aggies generally line up with four receivers and one running back with the quarterback in shotgun. In Sumlin’s offense, receivers run routes of all depths, but they often have two men run deep routes and the other two receivers attack underneath. The Aggies offense runs best when the quarterback is able to get the ball out quickly, while offensive line is counted on to pick up the pass rush with just five men.

That’s an oversimplification of how the Aggies run things, but you get the picture.

There are a few major differences between Manziel and Hill, who performed admirably until the last few weeks. Manziel had an NFL-caliber arm in college, allowing him to connect on those long passes with greater ease than Hill. Everyone thinks of the Aggies as this explosive downfield machine, and they do lead the conference in completions of 20-plus and 30-plus yards this season, but they’ve taken a step back this season.

In 2012 and 2013 both, more than 10 percent of the Aggies completions went for 30 or more yards; that figure has dropped to 7.1 percent this season. In 2012 and 2013 respectively, 19.1 and 22.7 percent of A&M’s completions were for 20-plus yards, and that’s dropped to 15.2 percent this season.

Those numbers also don’t take into account how many of the 20- and 30-yard passes this season started as screens and short throws that the receivers turned into longer gains after the catch. A lessened deep threat allows defenses to play the Aggies receiving corps tight at the line and complicate things for the offense.

Manziel had a reputation as a freelancer in college, which is a nice way of saying he often ran around until something opened up downfield. Hill is a capable runner when he has grass in front of him, but he’s not going to reverse course multiple times behind the line of scrimmage and throw a bomb on the run like Manziel did for the Aggies on so many occasions.

Manziel’s ability to break big runs is missing from this iteration of the Aggies offense as well. He rushed 144 times last season, picking up first downs on 44 of them and going for 10-plus yards 36 times.

So far this season, Hill has only taken off 52 times, putting him on pace for less than half the attempts Manziel had a year ago. He’s picked up first downs on 14 of those runs (26.9 percent to Manziel’s 30.5) and just nine have gone for 10 or more yards.

Not having Johnny Football’s elusiveness has only served to amplify the issues the offensive line has had this season. It’s hard to say that Manziel made his offensive linemen look better, since several of them are playing on Sundays now, but Hill isn’t doing his any favors.

A group with several touted NFL prospects, anchored by presumed top-10 draft pick Cedric Ogbuehi at left tackle, has been shaky. They’ve struggled against the tough defensive fronts they’ve faced in recent weeks, and that pressure has had a negative effect on Hill.

Arkansas, Mississippi State, Ole Miss and Alabama all rattled Hill with their pressure at one time or another. After playing nearly mistake-free football, Hill’s interception totals have spiked in the last few weeks as he’s seen pass rushes barreling toward him.

It’s possible that Sumlin’s offense needs a cannon-armed, mobile quarterback to function at its highest possible levels. A&M’s eight games this season have shown that there has, in fact, been a drop off once Manziel was removed from the equation.

There are starting to be grumblings that Hill isn’t the answer and that a change should be made. Freshman Kyle Allen, the nation’s top quarterback recruit a year ago, has a big arm, but it’s untested at the college level. (Allen has thrown 38 passes, mostly in garbage time.)

The shutout A&M suffered against Alabama last week is an aberration, given Sumlin’s track record as a head coach. The Aggies will get back to putting up big-time yardage and point totals sooner than later, most likely.

They need to figure out their math first, though.