Mistaken Assumption Basic to the Contract?

Kastoroff entered the contract under the mistaken belief that his figures added up to just under $90,000, when in fact they added up to just under $99,500.

The assumption was basic to the contract since the approximately $10,000 difference was quite significant (in 1960, the time of the case).

Kastoroff did not enter the contract under a mistaken assumption basic to the contract.

Kastoroff entered the contract under a mistaken assumption basic to the contract.