Human: Bill is trying to control the pests in his garden. Each spider he introduces eats 7 bugs, and each time he sprays the garden he reduces the total bug population to 80% of what it was previously. If the garden has 400 bugs to start, and Bill sprays once and introduces 12 spiders, how many bugs are left? Assistant: 
How many bugs are left after spraying? ** First find the total bug population after spraying: 80% * 400 bugs = <<80*.01*400=320>>320 bugs
How many bugs does each spider eat? ** Then find the total number of bugs each spider eats: 12 spiders * 7 bugs/spider = <<12*7=84>>84 bugs
How many bugs are left after introducing spiders? ** Then subtract that number from the number of bugs left after spraying to find final number of bugs: 320 bugs - 84 bugs = <<320-84=236>>236 bugs
#### 236