After 100 new people move into a town, 400 of the original population move out. Every year afterward, the town’s population is halved. After 4 years, the population is 60 people. Before the new people moved in, how many people lived in the town?
If the population is halving then at the end of the third year, the population must have been 60 people in the fourth year * 2 = <<60*2=120>>120 people.
In the second year, the population was 120 people in the third year * 2 = <<120*2=240>>240 people.
And in the first year, the population was 240 people in the third year * 2 = <<240*2=480>>480 people.
Additional people moved out in the first year, so accounting for these shows the population was 480 people + 400 people who moved out = <<480+400=880>>880 people.
Then removing the new people shows there were originally 880 people – 100 new people = <<880-100=780>>780 people.
#### 780