To find the total discount John received for buying the laptop, we need to calculate the discount he received both initially and as a member of the shop.
1. Initially, John received a discount of 10%. This means he paid only 90% of the original price.
Discounted price = Original price - (Original price x Discount percentage)
Discounted price = $900 - ($900 x 10%)
Discounted price = $900 - ($900 x 0.10)
Discounted price = $900 - $90
Discounted price = $810
2. As a member of the shop, John enjoyed an additional 10% discount on the discounted price he already paid.
Discounted price as a member = Discounted price - (Discounted price x Discount percentage)
Discounted price as a member = $810 - ($810 x 10%)
Discounted price as a member = $810 - ($810 x 0.10)
Discounted price as a member = $810 - $81
Discounted price as a member = $729
Now, let's calculate the total discount John received:
Total discount = Original price - Discounted price as a member
Total discount = $900 - $729
Total discount = $171
Therefore, the correct answer is not provided in the options. The total discount John received for buying the laptop is $171.