Mia has 4 times as many shells as David. Ava has 20 more shells than Mia. Alice has half the number of shells Ava has. If David has 15 shells, what the total number of conch shells they all have?
If David has 15 shells, then Mia has 4 *15 = <<15*4=60>>60 shells.
Ava has 20 more shells than Mia, so that is 60+20 = 80 shells.
Alice has 1/2 the number of shells Ava has, which is 1/2*80 = <<1/2*80=40>>40 shells.
The total number of shells all of them have is 15+60+80+40 = <<15+60+80+40=195>>195 shells.
#### 195