One is based on currency equivalents for the purposes of international trade. The other is based on what you can buy with that money locally.
The average annual wage in Egypt is 156,526 EGP, which is a little over $3,000 U.S.,, so in terms of income you can think of 3 EGP as being equivalent to 1 USD.
A typical car costs 500k EGP, which is under $10k U.S. So in those terms, you can thin of 10 EGP as being equivalent to 1 USD.
But in terms of currency conversion, it is about 51 EGP to the dollar, making goods bought from the U.S. anywhere from 5 to 17 times as expensive as they are from the perspective of someone living in the U.S.
This is why most store systems allow you to set different prices in different countries. $18 U.S. is a meal for one person here in the U.S., but enough money to feed a family for a week in many parts of the world.