The Missing Dollar

[mendhak]

I posted this in Chit Chat, but I think minds such as the ones here can tell me:

Two friends go to a small shop. They decide to purchase a small radio/cassette player for $50. They each pay $25 and take it away.

The shopkeeper suddenly remembers that the cost of the radio was actually $45, so he sends his assistant along with $5 to give back to them. The assistant thinks to himself, "What the hey, I'll keep $2 with me." The assistant catches up to the two friends and gives them $3, and goes back.

Now, each friend had paid $25, and they got $1.5 back, each.

25-1.5 = 23.5. So, they each paid $23.5 for the radio.

Combined, they paid...$23.5 + $23.5 = $47 for the radio.

There's $2 in the assistant's pocket.

$47 + $2 = $49.

Wait a minute, they paid $50....
Where is the missing dollar?

??

Edit: Serious answers please.