Less —
1. Sentences like “No less than 20 boys competed for the prize” are sometimes set for correction. Perhaps the paper-setters want fewer for less, because they read in a familiar book of English Grammar by an Englishman that few denotes number and little denotes quantity. But a reference to the Pocket oxford Dictionary will give them the following : "Less- a less quantity, fewer (opp. more: less noise please; had less men killed but more wounded).
2. Pron. A less amount, a less quantity of something or number of things or persons (cannot take less; less than 20 of them remain)". So. there is no mistake in the sentence given in the first line.
