Andy estimated that he would need 77 feet of lumber for a tree house project. he later found that the actual amount of lumber needed was 66 feet. what was the percent error of andy's estimation?

Aquantity with an initial value of 3900 decays exponentially at a rate of 35% every hour. what is the value of the quantity after 0.5 days, to the nearest hundredth?

The distribution of the amount of money spent by students for textbooks in a semester is approximately normal in shape with a mean of $235 and a standard deviation of $20. according to the standard deviation rule, how much did almost all (99.7%) of the students spend on textbooks in a semester?

X+y=-4 x-y=2 use elimination with adding and subtraction