The density of water at 20°C is 998 kg/m3  and 40°C 992 kg/m3. The coefficient of volume expansion of water is

As ρT2=ρT1(1+γΔT)=ρT11+γT2-T1  Here, T1=20°C,T2=40°C ρ20=998 kg/m3,ρ40=992 kg/m3 ∴  992=9981+γ(40-20)                992=9981+20γ 992(1+20γ)=998 1+20γ=998992   or   20γ=998992-1=6992 γ=6992×120=3×10-4/C  ∘