Addition or Subtraction - LCM TricK

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Shortcut

• “Subtracting k, the number becomes divisible” → LCM + k


• “Adding k, the number becomes divisible” → LCM − k

Q. Find the smallest number which, when 7 is subtracted from it, is exactly divisible by 12, 16 and 18.

Solution: 

1st: Find LCM

LCM (12,16,18) = 144

2nd: 7 is subtracted

So, add 7 to the LCM: 144 + 7 = 151

Ans: 151

Note: Subtract → Add,  Add → Subtract

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