Observe the following table and determine the missing number in the last cell: A | B | C | D | Result 5 | 2 | 3 | 10 | 40 4 | 3 | 5 | 8 | 40 6 | 4 | 2 | 12 | ?

Correct — B.
Rule: Result = 2 × (A + B + C + D).

Row 1: 5 + 2 + 3 + 10 = 20, and 2 × 20 = 40 ✓
Row 2: 4 + 3 + 5 + 8 = 20, and 2 × 20 = 40 ✓

Row 3: 6 + 4 + 2 + 12 = 24
2 × 24 = 48 → option (b).

Why the others are wrong

• (a)
  72 — 72 comes from a rule that leaves two columns unused, such as D × (B + 2): 10 × 4 = 40 and 8 × 5 = 40, then 12 × 6 = 72. The key takes the rule that uses all four numbers.
• (c)
  50 — 50 would need the third row to add up to 25. It adds up to 6 + 4 + 2 + 12 = 24, and twice that is 48.
• (d)
  25 — 25 is odd, but the rule doubles a whole-number sum, so every result it gives is even. Twice the third row's sum of 24 is 48.

A table puzzle hides one rule that turns each row's inputs into its result. Test a candidate rule on every complete row before using it on the row with the gap.

Here the two complete rows reach 40 from different numbers, yet both add up to 20. That shared total is the clue: the result is twice the row's sum.

Key facts

• Rows 1 and 2 both add up to 20, and both results are 40.
• Row 3 adds up to 24, so its result is 2 × 24 = 48.
• Twice a whole number is always even, which rules out 25 at once.

Common traps

• Fitting a rule to one row and applying it without checking the other
• Settling on a rule that leaves columns unused, such as D × (B + 2), which leads to 72

No directly related past PYQ was found.