Edna made cookies for all of her neighbors and left the cookies outside for them to take. She made 150 cookies so her 15 neighbors could get 10 cookies each. However, the neighbor who arrived last told Edna there were only 8 cookies left. Edna thinks it was Sarah who took too many cookies. If all the other neighbors took the correct amount of cookies, how many cookies did Sarah take? Let's think first. Chain of thought:
Sarah and the final neighbor took the wrong amount, which means that 15 neighbors – 1 Sarah – 1 final neighbor = 13 neighbors took 10 cookies each. This is a total of 13 neighbors * 10 cookies = 130 cookies taken by the first 13 neighbors. There were only 8 cookies left, so that means the first 13 neighbors and Sarah took a total of 150 – 8 = 142 cookies. So Sarah must have taken 142 – 130 = 12 cookies.
Therefore, the answer is 12.