To decrease an amount by 70%, what single multiplier would you use? how do i work this out?

To decrease an amount, you would multiply it by 0.30. you multiply it by 0.30 because this gives you 30%; therefore, it has been decreased by 70%. To decrease an amount, you always times it by 0. and then whatever the remainder is. If you were decreasing 'y' by 65%, you would work it out by doing y * 0.35