Maybe, maybe not - it depends on how related the actions are and if you consider "possible" to be "desirable". For example, if printing was done to the same place then the output would be interleaved and would appear corrupted. This can happen easily when the same buffer is used by all threads. So yes, it is possible, but you might not get what you want.

Adding two numbers is also not a simple as it first appears. First, of course, each thread must retain its own result. If you then require a summation then a "sweeper" thread must access each worker thread's result to produce the sum. Not everything can be made parallel, see Amdahl's law.