Study the series: Q 6 * D 2 F 9 ! H 5 & 3 K L 8 J ? 7 M 4. How many digits in the series are each immediately preceded by a letter and immediately followed by a symbol?

Take the digits one by one. 6 has Q before it and * after it — counts. 2 has D before it but F after it — fails. 9 has F before it and ! after it — counts. 5 has H before it and & after it — counts. 3 has the symbol & before it — fails at once. 8 has L before it but J after it, 7 has ? before it, and 4 has M before it but nothing after it. So only 6, 9 and 5 satisfy both halves of the rule, giving 3. Answering 2 means one of the three was missed; 4 and 5 come from letting a digit through on the strength of its left neighbour alone.