insert formula in many sheets

I have a book with twenty sets ofsheets Each 20 sets has 4 sheets. I would like to place a formula into all twenty sets of four but only into the 2nd sheet of each set. Is there an easyer way then going to each sheet to put in the formula.

If the formula you're going to enter is in the same cell on all 20 sheets, the easiest way would be to hold down the CTRL key and then click on the 20 sheet tabs you want to modify. This will select them as a group, so that any change you make to one sheet will also be made on the other 19. Once you're done adding the formula, be sure to click on another sheet tab (or right-click one of the selected sheet tabs and choose "Ungroup sheets", otherwise you'll keep changing all 20 sheets at once - possibly unintentionally).