If 'P' denotes '+', 'Q' denotes '×', 'R' denotes '−', and 'S' denotes ‘÷’ what is the value of the following expression? 6 Q 2 P 4 R 3 S 1 =?

Correct — B.
Rule: replace each letter by its sign, then apply BODMAS: × and ÷ before + and −.

6 Q 2 P 4 R 3 S 1 = 6 × 2 + 4 − 3 ÷ 1
6 × 2 = 12 and 3 ÷ 1 = 3
12 + 4 − 3 = 13 → option (b).

Why the others are wrong

• (a)
  16 — 16 is 12 + 4 with the final − 3 ÷ 1 left off. That term is 3, and it still has to be subtracted.
• (c)
  12 — 12 is only the first product, 6 × 2. The + 4 and the − 3 still have to be applied.
• (d)
  10 — 10 is 3 short of the true value. After 6 × 2 + 4 = 16, only 3 ÷ 1 = 3 comes off, leaving 13.

A letter-for-sign item is two jobs in a fixed order. First decode: P is +, Q is ×, R is −, S is ÷. Write the plain expression out in full before touching a number.

Then evaluate by BODMAS: division and multiplication first, working left to right, then addition and subtraction.

Here 6 × 2 and 3 ÷ 1 are done first, leaving 12 + 4 − 3.

Key facts

• Decoded, the expression reads 6 × 2 + 4 − 3 ÷ 1.
• BODMAS order: brackets, then division and multiplication, then addition and subtraction.

Common traps

• Working strictly left to right. It happens to give 13 here, but it goes wrong whenever a × or ÷ follows a + or −.
• Mixing up the letters for − and ÷ (R and S).

No directly related past PYQ was found.