The effective discount is not simply the sum of the individual discounts, i.e., it is not 10% (shopkeeper`s discount) + 10% (e-wallet cashback) = 20%. This is because the second discount of 10% is applied after the first discount has already been deducted.

So, in actuality, the calculation would be:

The first discount of 10% reduces the price to 90% of the original.

Then, a further discount of 10% on this reduced price further reduces it to 90% of the already reduced price.

Mathematically, the effect of both discounts combined can be calculated as follows:

0.90 (after the first discount) * 0.90 (after the second discount) = 0.81.

This means that the customer is effectively paying 81% of the original price. Therefore, the effective discount is 100% - 81% = 19%.

Hence, the correct answer is option 3: 19%. Options 1, 2, and 4 are not correct because they do not correctly account for the compounding effect of the two discounts.