Yes, your phrase is correct, however, you might also try:

“If you add one AND three, they make four”

“If you add one to three, it makes four”

Or alternately, how about re-phrasing:

“The sum of one and three are four”

Or simply:

“One plus three is four”

You might also say:

“If you add one two three, it would make four”

But that would be incorrect, because one + two + three make five. : ) : )

Or ” If you add one to three, you will get four.”

Keep sentence in the active voice using same subject.– assuming that you are giving instructions.

I agree with the person who answered first……..

If you add one to three, it makes four…….

first of all, i think of the real grammar purist — by ability of definition — could by no ability nicely known the “that’s me” as standard English, yet easily in spoken English no possible dare proper somebody for asserting that. even nonetheless, i’m particular that for the duration of a extreme college or college someplace, there’s a instructor who’s attempting to do his/her bit and coach the right form. i became taught back in worry-free college (by ability of nuns) to respond to “that’s she” whilst somebody asks for me on the telephone, and that i nonetheless do it to on the present time for stress of habit. many times, i think that archaic grammar types must be whipped out for dramatic result now and returned and additionally to place people of their places, that’s often ineffective considering the fact that they only think of my grammar is undesirable! could that the traditional American have been waiting to understand the placed-down! 😛 area be conscious to Mouth: “Me” or “I” is easily no longer an merchandise in this sentence; that’s a concern supplement following a linking verb to describe the priority “it”, that’s why it would be “I”…that’s the place the completed debate starts off! 🙂 …

I wouldn’t use “make” or “is.”

One plus three equals four.

you can say it MAKES four

but otherwise i dont see any problem with it

yes.