This question involves solving two distinct percentage calculations and then adding them together. Let`s dissect each option.

Option 1- 10 per cent of 20: This is accurate but it`s only half of the equation. We also need to add 20 per cent of ten.

Option 2- 20 per cent of 20: This is the correct answer because 10 per cent of twenty is 2 and 20 per cent of ten is also 2. The sum of both is 4, which is exactly 20 per cent of 20.

Option 3- 1 per cent of 200: This results in 2, which is just one part of our equation (10 per cent of 20 or 20 per cent of ten).

Option 4- 2 per cent of 200: This result is equivalent to either 20 per cent of 10 or 10 per cent of 20, not the sum of both.

So, the answer of 20 per cent of 20, choice 2, is correct because it represents the total value when combining 10 per cent of twenty and twenty per cent of ten.