At a driving-test centre the pass rate rose from 60% to 75% after new practice sessions were started. By what per cent did the failure rate fall?

The failure rate went from 100 - 60 = 40% down to 100 - 75 = 25%. The fall of 15 must be measured against the EARLIER failure rate: 15/40 = 0.375 = 37.5%. 15% is the drop in percentage points read as a per cent fall. 25% quotes the new failure rate rather than the change. 60% divides by the new failure rate (15/25) instead of the old one. Note how a modest 15-point gain in passes cuts failures by well over a third - the failure base is the small one.