Kris is blowing u balloons for her sister's party. She has 30 minutes to blow up as many balloons as possible and decides to enlist her brother's help to increase the number of balloons. Kris can blow up a total of 2 balloon per minute, and her brother works twice as fast. After 15 minutes, her brother doubles his speed and works at this new speed for the remaining 15 minutes. After the 30 minutes, how many balloons, in total, did Kris and her brother blow up?
Let's think: Throughout the 30 minutes, Kris blows up 2 balloons per minute * 30 minutes = 60 balloons. Her brother works at double Kris' speed in the first 15 minutes so he works at 2 balloons per minute * 2 = 4 balloons per minute. So in the first 15 minutes, he blows up 4 balloons per minute * 15 minutes = 60 balloons. In the second 15 minutes, he is working at double the rate he did previously, so he blows up 4 balloons per minute * 2 = 8 balloons per minute. In the second 15 minutes, Kris' brother therefore blows up 8 balloons per minute * 15 minutes = 120 balloons. Throughout the 30 minutes, he has blown up a total of 60 + 120 = 180 balloons. Kris and her brother therefore blew up a total of 60 balloons from Kris + 180 balloons from Kris' brother = 240 balloons.. The answer is: 240.

Brennan was researching his school project and had to download files from the internet to his computer to use for reference. After downloading 800 files, he deleted 70% of them because they were not helpful. He downloaded 400 more files but again realized that 3/5 of them were irrelevant. How many valuable files was he left with after deleting the unrelated files he downloaded in the second round?
Let's think: The number of non - valuable files Brennan downloaded in the first round is 70 / 100 * 800 = 560 files. The number of valuable files Brennan downloaded in the first round is 800 - 560 = 240. When he downloaded 400 new files, there were 3 / 5 * 400 = 240 non - useful files, which he deleted again. The total number of valuable files he downloaded in the second round is 400 - 240 = 160. To write his research, Brennan had 160 + 240 = 400 useful files to reference to write his research.. The answer is: 400.

Alex has 2 cakes that are each cut into 8 slices. A fourth of the slices are given away to his friends. A third of the remaining slices are given away to his family. Alex eats 3 slices. How many slices of the cake are left?
Let's think: There are 2 * 8 = 16 slices of cake. There are 16 / 4 = 4 slices. There are 16 - 4 = 12 slices left. There are 12 / 3 = 4 slices given away. There are 12 - 4 - 3 = 5 slices of cake left.. The answer is: 5.

There are 40 more buyers in the grocery store today than yesterday. There were half the number of buyers yesterday as there were the day before, and the day before had 50 buyers. Nobody visited the store on more than one day. What's the total number of buyers who've visited the store in the three days?
Let's think:
If yesterday the number of buyers was half the number of buyers the day before, then yesterday there were 1 / 2 * 50 = 25 buyers. Today has 40 more buyers than yesterday, so there were 40 + 25 = 65 buyers today. The total number of buyers in the store for the three days will be 65 + 25 + 50 = 140 buyers.. The answer is: 140.