1. **Problem statement:** A pressure gauge connected to a tank reads 3.5 bars, and the barometric pressure is 75 cm Hg. We need to find the absolute pressure in the tank. 2. **Formula and concepts:** Absolute pressure is the sum of gauge pressure and atmospheric pressure: $$P_{absolute} = P_{gauge} + P_{atmospheric}$$ - Gauge pressure is the pressure above atmospheric pressure. - Atmospheric pressure must be converted to the same units as gauge pressure. 3. **Convert atmospheric pressure from cm Hg to bars:** - 1 atm = 76 cm Hg = 1.01325 bar - So, 1 cm Hg = \frac{1.01325}{76} bar Therefore, $$P_{atmospheric} = 75 \times \frac{1.01325}{76} = 1.0 \text{ bar (approximately)}$$ 4. **Calculate absolute pressure:** $$P_{absolute} = 3.5 + 1.0 = 4.5 \text{ bars}$$ 5. **Answer:** The absolute pressure in the tank is **4.5 bars**.