Nonlinear calculations on ouputs of margin commands

[Jenny Cui]

I have two margin results from two separate OLS regressions with the following command:

reg w2_a c.lny2##(c.n_woman c.n_man c.n_child i.district)
margins, dydx(lny2)

reg w2_c c.lny2##(c.n_woman c.n_man c.n_child i.district)
margins, dydx(lny2)

where w2_a and w2_c are budget shares for adults and children in each household, lny2 is the log total budget, n_woman is the number of women in the household, and i.district is the district dummy.

Denote the margin output of the first regression by M1 and the second by M2. What can I do if I want to calculate M2/(M1+M2) and its inferences? I have tested that (M1+M2) is significantly different from zero.

Thanks for your help!