Read the sequence below, which runs from left to right and holds twenty-three elements: 7 M % K 4 B @ P 2 W & 9 T F # 5 J R $ 6 D N 8. How many letters in it have a digit standing immediately before them and a symbol standing immediately after them?

Both conditions must hold at once. M has 7 before it and % after it; B has 4 before and @ after; W has 2 before and & after — three letters in all. Six letters have a digit before them (M, B, W, T, J, D), so 6 is what you reach by checking only the first condition; five letters have a symbol after them (M, B, W, F, R), so 5 is what you reach by checking only the second. T, J and D each have the digit before but a letter, not a symbol, after; F and R each have the symbol after but a letter before. Dropping any one of the three genuine hits gives 2.