Alright guys, just looking for a point in the right direction for a tutorial question. GIVEN VALUES: Temperature change with increasing altitude: 0.0065 K/m Temp at sea level: 15ºC Pressure at sea level: 101.5 kPa FIND: Atmospheric pressure at 7500m. So what I've done is found the temperature decrease between sea level and 7500m, so that temperature is 239.4K. And then tried (P1/T1)=(P2/T2), was a bit sceptical over this working.. it didn't. After that tried: ∫(1/P) dP = -∫(g/RT) dz Integrated that, giving: ln(P2/P1) = (-g/RT)(z2-z1) Placed in the values given/calculated, leading to: P = 101500*e^[(-9.81*7500)/(287*288.15)] P = 41.7 kPa ... which is a wee bit off the stated answer of 38.3 kPa. Any ideas?