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## Homework Statement

On a warm day, a student uses a tire gauge to test the air pressure of her tires. While listening to the weather report on the way to the garage, she finds that the barometric pressure is 780mmHg. If the gauge reads a pressure of 35psi, what is the

*actual*pressure inside the tires in psi?

## Homework Equations

I don't know which equation I should be using. Is it a trick question because the tyre pressure doesn't change or is it

*P*

**gauage**= P**absolute**- P**ambient**## The Attempt at a Solution

if it is then I'm assuming that absolute pressure is the same as actual pressure.

Then

*P*= 35psi

**gauage***P*= 780mmHg= 15.0868psi

**ambient**and I have to find

*P*

**a**which would be

*P*=35 + 15.0868

**absolute**= 50.868 psi

Like I said I have no idea....thanks!