<human>:  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?
<bot>: How many shells does Mia have? ** If David has 15 shells, then Mia has 4 *15 = <<15*4=60>>60 shells.
How many shells does Ava have? ** Ava has 20 more shells than Mia, so that is 60+20 = 80 shells.
How many shells does Alice have? ** Alice has 1/2 the number of shells Ava has, which is 1/2*80 = <<1/2*80=40>>40 shells.
What is the total number of shells they all have? ** The total number of shells all of them have is 15+60+80+40 = <<15+60+80+40=195>>195 shells.
#### 195