A loan of $1,200 at 5.30% p.a. flat over 2 years has monthly instalments of $55.30. What effective rate of interest per annum is being charged (as a %, 2 decimal places)? When calculating the monthly rate, use linear interpolation with no more than a 0.25% gap between the higher and lower estimates.
(The answer required is j1 and not the monthly rate and not j12.
The rough approximation (2 x flat rate) / 12 will help you find suitable starting estimates for the monthly rate in your linear interpolation.)