I need function to calculate the reverse of adding percent margin to a number
(e.g. product price).

For example, I have a number 100, and I want to identify the number that
will result in 100 after 40% deduction (discount).
I am looking for a formula or function in excel that will result in 166.67.
Note that 166.67 - (166.67 * 40%) will result in my original number of 100.
Some business calculator has this function (label as MU for Citizen
calculator). Anyone knows how does Excel handles this, or know of a formula
that can handle this.

Another example is: The formula that will return 250 after input of 100 and
60% discount. That is 250 - (250 * 60%).

Note that in my 2 example, the inputs are 100 and 40% with result of 166.67,
and 100 and 60% with result of 250.

Thanks a lot..