An electroscope is a device that detects charge on objects that touch it or are brought near it. john rubs a piece of cotton fabric on a plastic rod and then touches the rod to the electroscope.

what methods of charging does john use?

are there answer choices to this question? this seems like a question where you have options to choose from.

the old price per ounce is c/4.

the new price per ounce is c/3.6.

the ratio of the old price to the new one is

(c/4)/(c/3.6) = (c/c)×(3.6/4) = 0.9 . . = 9/10 . . "nine tenths" in either form