Calculate IPL Run Rate from Overs and Balls
To calculate run rate, convert displayed overs into a valid-ball count first. A display of 8.3 is eight overs and three balls, which is 8.5 overs for arithmetic.
Convert the notation
Eight completed overs contain 48 valid balls. Add the three balls shown after the point to get 51. Divide 51 by six to get 8.5 mathematical overs. Using 8.3 as a decimal would produce the wrong rate.

Apply the calculation
For an illustrative 85 runs after 8.3 displayed overs, divide 85 by 8.5. The current run rate is 10 runs per over. It describes the innings so far and does not predict the next over or the eventual total.
Separate current and required rates
A chase can show a required rate based on the remaining target and balls. That is a different calculation from the current scoring rate. Use the current target and any revised innings allocation, especially after an interruption.
A useful next step
Use the IPL page for match context and the official scorecard for real values. Keep illustrative calculations separate from a live result.