When a quantity increases by 25%, the new quantity becomes 100% + 25% = 125% of the original quantity.
After the first year, the quantity has increased to 125% of its original value. After the second year, it increases an additional 25%, making the new value 125% + (25% of 125%) = 156.25% of the original value. Finally, after the third year, it increases by another 25%, making the new value 156.25% + (25% of 156.25%) = 195.3125% of the original value.
So the quantity has increased by 195.3125% - 100% = 95.3125% over the three-year period. Therefore, the combined percentage growth p over the three-year period is 95.3125%.