In the sequence R+JM2$#QR?*O@7F3, how many symbols are there that are immediately preceded by a number?

Introduction / Context:
This question falls under symbol and number based reasoning. The focus is not on arithmetic but on carefully scanning a mixed sequence of letters, digits, and special symbols to count how many symbols satisfy a particular positional condition. Such questions test attention to detail and accuracy in reading complex strings.

Given Data / Assumptions:

• The sequence given is R+JM2$#QR?*O@7F3.
• We treat digits (0 to 9) as numbers and characters like plus, dollar, hash, question mark, star, and at sign as symbols.
• The task is to count how many symbols are immediately preceded by a number directly to their left.
• Only adjacency matters; we do not look at characters further away.

Concept / Approach:
The procedure is simple but requires discipline. We scan the sequence from left to right, identify each symbol, and then check the character immediately to its left. If that character is a digit, we increase our count. Finally, we compare our count with the given answer choices.

Step-by-Step Solution:
Step 1: Write the sequence with indices: R(1), +(2), J(3), M(4), 2(5), $(6), #(7), Q(8), R(9), ?(10), *(11), O(12), @(13), 7(14), F(15), 3(16). Step 2: List the symbols: +, $, #, ?, *, @. Step 3: Check each symbol and the character immediately to its left. For + at position 2, the previous character is R, which is a letter, so this does not qualify. For $ at position 6, the previous character is 2 at position 5, which is a number. This is one valid case. For # at position 7, the previous character is $ at position 6, which is a symbol, not a number. For ? at position 10, the previous character is R at position 9, a letter. For * at position 11, the previous character is ? at position 10, a symbol. For @ at position 13, the previous character is O at position 12, a letter. Step 4: Only the dollar symbol after the digit 2 is immediately preceded by a number, so the count is 1.

Verification / Alternative check:
To verify, we can quickly re scan and mark only positions where a digit is followed by a symbol. The substring 2$ is the only occurrence of digit followed by symbol. The digit 7 is followed by F, which is a letter, not a symbol. Therefore, one is the only correct count.

Why Other Options Are Wrong:
Options 4, 3, and 2 imply that multiple symbols satisfy the condition. However, there is no other symbol that immediately follows a digit apart from the dollar symbol. Hence, those counts are overestimates based on misreading the sequence. The none of these option fails because the count one is explicitly present as an option.

Common Pitfalls:
Students may misclassify letters or symbols or forget that the condition is specifically about being immediately preceded by a number, not simply occurring somewhere after a number. In long sequences, skipping positions or double counting are common mistakes. Writing the sequence with indices and checking each symbol in order helps maintain accuracy.

Final Answer:
Exactly 1 symbol is immediately preceded by a number.