\(PV=nRT\)
\(V_1=\dfrac 4 3 \pi \left(\dfrac {50}{2}\right)^3 \\ V_2 = \dfrac 4 3 \pi \left(\dfrac {51}{2}\right)^3 \\ \mbox{The rest of the quantities other than temperature stay constant.} \)
\(\dfrac{P V_1}{P V_2} = \dfrac{n R T_1}{n R T_2} \Rightarrow \dfrac {V_1}{V_2}=\dfrac {T_1}{T_2}\)
\(\dfrac {V_1}{V_2}=\dfrac{50^3}{51^3} = \dfrac {125000}{132651} \\ \mbox{so }\dfrac {T_1}{T_2} = \dfrac {125000}{132651} \\ T_2 = T_1 \dfrac{132651}{125000} = 19 \dfrac{132651}{125000} = 20.163 ^\circ C\)
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