Since the population of Mojave has increased three times the number it was a decade ago, there are 3*4000 = <<3*4000=12000>>12000 people in Mojave now.
It's predicted that the population will increase by 40/100*12000 = <<40/100*12000=4800>>4800 people after five years.
This means there will be 12000+4800 = <<12000+4800=16800>>16800 people living in Mojave in five years.
#### 16800