Total number of days =30
Number of days for which the concentration of Sulphur dioxide was in the interval of 0.12 −0.16= 2
P(concentration of Sulphur dioxide in the interval 0.12 - 0.16)=Number of days for which the concentration of Sulphur dioxide was in the interval of 0.12 - 0.16Total number of days
Hence, required probability, P=230=115