Gauge pressure at the bottom of a barrel

[Of Mike and Men]

Homework Statement

A barrel contains a 0.110 m layer of oil and a density of 690 kg/m3 floating on water that is 0.300 m deep. What is the pressure at the bottom of the barrel?

Homework Equations

The Attempt at a Solution

Poil + Pwater = Ptotal

My question is why am I using this formula? I got the correct answer, but initially I wanted to treat the pressure of the water as a negation of the pressure of the oil, causing the barrel to float. So, Poil - Pwater. Is the reason for the addition because I am treating the bottom of the barrel as a point and the pressure acting on it in every direction equally and taking my gauge pressure from that exact point?

Thanks

 

[CWatters]

My question is why am I using this formula? I got the correct answer, but initially I wanted to treat the pressure of the water as a negation of the pressure of the oil, causing the barrel to float.

My reading of the question is that both the oil and the water are in the barrel.

 

[Of Mike and Men]

My reading of the question is that both the oil and the water are in the barrel.

Okay, thank you. I mis-read that. I was assuming the barrel was floating on the water. Paying attention to sentence structure is useful.