(7+5)-2=(5+7)-2 what property is this? ?

Any greatly appreciated! you in advance. jody bought 20 shares of amazon at the close price of $121.00. she bought 20 more shares a year later at the price of $127.00. two years later she's sold all of her shares at the price of $133.00. her broker charges $50 for each transaction. after all of these transactions how much money did jody make? a.$65.00b.$5288.00c.$210.00d.$310.00

You give a $4 tip for a meal that cost $22. approximately what percent of the bill was your tip?

The? half-life of a radioactive substance is 20 years. if you start with some amount of this? substance, what fraction will remain in 120 ? years