. If a substance has an excess number of electrons on its surface, what type of charge does it have?
A positive charge.

A negative charge.

A neutral charge.

A nuclear charge.

A negative charge

Explanation:

If there is an excess of electrons in a substance, this will have a negative net charge. This is because electrons have negative charge

q = -1.67*10^{-19}

each electron will contribute with this charge to the total negative net charge of the substance.

hence, the answer is "A negative charge"

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