If $10$ men can complete a wall in $8$ days, how many men are needed to complete it in $4$ days?

If $10$ men can complete a wall in $8$ days, how many men are needed to complete it in $4$ days?
  1. $15$
  2. $18$
  3. $20$
  4. $24$

Solution

$10 \times 8 = m \times 4 \Rightarrow m = 20$.

Asked in: IMO

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