<em>The error in the sentence is using double negatives.</em>
Explanation:
Yes, there is a mistake in this sentence. The error is using double negatives in the same sentence. Double negative is making use of two negative words in a phrase like “I didn’t do nothing”, but in this double usage of negatives words they are canceling each other as if it is affirming that “I did something”. The correct construction for the sentence above should be “I don’t know about the kind of machines used to make roads.” or “I know nothing about the kind of machines used to make roads.”
