× 3 1 2 4 □ □ □ The above shows an incomplete long multiplication. Each square represents a single digit.
A possible way to complete this is 1 7 × 2 0 = 3 4 0 . Is this the only possible way?
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I chose "No" and it said "Incorrect"...
1 2 × 2 9 = 3 4 8 is the third and final possible way.
15 23=345 and 12 29=348
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Two more solutions exist 1 5 × 2 3 = 3 4 5 , 1 2 × 2 9 = 3 4 8 Writing problem as 1 A × 2 B = 3 4 C ⟹ 1 0 ( 2 A + B ) + A B = 1 4 0 + C Observe that 1 4 0 ≤ 1 0 ( 2 A + B ) + A B < 1 5 0 ⟹ 1 4 ≤ 2 A + B + 1 0 A B < 1 5 As the largest possible value of A = 7 giving us 0 ≤ B < 1 ⟹ B = 0 and since 1 0 = 2 × 5 and if B = 5 then A isnot integer (from above inequality ). Therefore A = 5 and then 4 ≤ B + 2 B < 5 ⟹ 8 ≤ 3 B ≤ 1 0 . Giving only possible B = 3 . For B = 2 does not hold good for 6 0 ≤ 1 1 A < 6 5 meaning A = 2 and 1 0 ≤ B + 5 B < 1 1 ⟹ 5 0 ≤ 6 B < 5 5 giving us next possible value B = 9 .
Thus, 1 7 × 2 0 = 3 4 0 , 1 5 × 2 3 = 3 4 5 , 1 2 × 2 9 = 3 4 8 and the answer is yes