inverse of 'predict' function

Question

Using predict() one can obtain the predicted value of the dependent variable (y) for a certain value of the independent variable (x) for a

Answer 1

Saw the previous answer is deleted. In your case, given n=50 and the model is binomial, you would calculate x given y using:

f <- function (y,m) {
  (logit(y/50) - coef(m)[["(Intercept)"]]) / coef(m)[["x"]]
}
> f(30,model)
[1] 48.59833

But when doing so, you better consult a statistician to show you how to calculate the inverse prediction interval. And please, take VitoshKa's considerations into account.