There is no fixed rate since it will depend on Ether price at the moment of transaction. The smart contract will use an oracle to keep constant track of Ethereum price and will send back the exact number of CTT that a user has purchased.
For example, in Ether price is $700.00, a transfer of 1 Ether to the smart contract address during the pre-ICO will result in the purchase of 3500 CTT (at $0.20 each). However, if Ether price had been $710.00, the user would have received 3550 CTT. This way everyone gets what they have paid for and possible swings in the market won’t have a negative impact.
The source that the smart contract will use to keep track of Ether price will be cryptocompare.com