5+38=43 25+38=20+(5+38)=20+43=63 55+38=50+(5+38)=50+43=93。

42+8=50 42+ 18=(42+8)+ 10=50+ 10=60 42+48=(42+8)+40=50+40=90。

19+7=26 19+37=( 19+7)+30=26+30=56 19+77=( 19+7)+70=26+70=96。

(1) multiplication principle: if the dependent variable f is in direct proportion to the independent variable X 1, X2, X3...Xn, and each independent variable is qualitatively different, if any independent variable f is missing, it will lose its meaning, then it is multiplication.

(2) addition principle: If the dependent variable F and the independent variable (z 1, z2, z3…,? Zn) is directly proportional to each other, and each independent variable has the same mass. If the dependent variable f still makes sense without any independent variables, it is addition.