Confused 4th grader

I found the definition of this standard as:

MAFS.4.OA.1.B

Your example above specifies addition, but the standard seems to include all four operations (+, -, x, ÷).

I was able to find this Common Core Map: https://www.khanacademy.org/commoncore/grade-4-OA  

The exercises here all seem to involve multiplication.

I looked back at the Operational and Algebraic Thinking standards for grades 3 and 2 to see whether there was more basic, foundational information and I found this video:

https://www.khanacademy.org/math/cc-2nd-grade-math/cc-2nd-add-subtract-100/cc-2nd-add-sub-miss-value-prob/v/missing-numbers-in-addition-and-subtraction-within-100

and these exercises:

https://www.khanacademy.org/math/cc-2nd-grade-math/cc-2nd-add-subtract-100/cc-2nd-add-sub-miss-value-prob/e/find-the-missing-number-add-sub-within-100

https://www.khanacademy.org/math/3rd-engage-ny/engage-3rd-module-2/3rd-module-2-topic-e/e/find-the-missing-number--addition-and-subtraction-within-1000-

This video covers multiplication and division:

https://www.khanacademy.org/math/cc-third-grade-math/imp-multiplication-and-division/imp-more-with-1-digit-multiplication-and-division/v/unknowns-with-multiplication-and-division

I hope this helps.