Given:
2 years ago - consumer price index 1,200 per month
current year - consumer price index 1,400 per month
Inflation rate = [(Consumer price index current - Consumer price index previous) / Consumer price index previous ] * 100%
Inflation rate = [(1400 - 1200) / 1200] * 100% = (200 / 1200) * 100% = 16.67%
Since 2 years has passed, the 16.67% inflation rate is good for 2 years. We simply divide the inflation rate by 2 to get the annual inflation rate.
16.66% / 2 = 8.33%
The annual inflation rate for the past two years is 8.33%