Actually as Paresh mentioned, 30%+10%=40% actually does not make any sense out of context :)
Your calculation is actually a weighted average port folio return.
Say you have 300 and divide that into 'equal' parts of 100 each (call this 'ticket' size of an investment) and invest in 3 stocks, say A, B and C.
At the end of the financial year you see A has gained 10%, B 5% and C 7%. Your portfolio gain will be 1-'ticket size'*(.10+.05+.07)=portfolio gain. Where all investments have same weight because their 'ticket size' is same.
On the other hand, if you have invested unequal 'ticket sizes', then you have to multiply each of the return % with its weight and multiply by entire portfolio investment capital.
There is no specific term that I have come across, it is just weighted average portfolio return.