Final answer:
The error in the given statement is the incorrect usage of the word 'less' instead of 'fewer'.
Step-by-step explanation:
The error in the given statement is the incorrect usage of the word 'less'. Instead, the correct word to use would be 'fewer'. The word 'less' is used to compare quantities that cannot be counted, while 'fewer' is used to compare quantities that can be counted.
For example, we say 'I have less water' because water cannot be counted, but we say 'I have fewer books' because books can be counted. In this case, the student should have said 'I left fewer questions blank than I did last time'.
By using the correct word, the sentence will be grammatically accurate and convey the intended meaning.