MATH PUZZLE: Can you replace...

A rabbi, a priest and a minister have their houses of worship side by side, so they decide to carpool.
On the first day, the other two are shocked to see the pastor lay hands on the hood and pray silently.
"What are you doing?" the priest asks.
The pastor looks up. "I'm just dedicating the car to the Lord's service."
"Good idea! Be right back!" the priest exclaims, running into his church. He emerges with a bulb on a short stick, shaking water out of it onto the car.
The rabbi stares. "What are you doing?" he says.
"I'm consecrating it with holy water," the priest replies.
"Great idea!" the rabbi says, and runs into his synagogue's toolshed. He emerges with a hacksaw and takes off an inch of the tailpipe.