How can you quickly calculate 20 percent of any bill amount?

What is the nth term rule of the linear sequence below? 27 , 25 , 23 , 21 , 19 , . .

Ann and betty together have $60 ann has $9 more than twice betty’s amount how much money dose each have

Aswimming pool had 2.5 million liters of water in it. some water evaporated, and then the pool only had 22 million liters of water in it. what percent of the water evaporated?