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If the sum of three consecutive integer is 51,
(n-1) + n + (n+1) = 51,
then
3n = 51, n = 51/3 = 17,
which means that the middle number of the three is 17, one third of the given sum.
Hence, Romania won 16 medals, China won 17 medals and U.S. won 18 medals. ANSWER
The lesson to learn from the solution is THIS :
If you are given the sum of three consecutive integer numbers, then the middle number is one third of the sum,
and you can quickly calculate it mentally without writing any equation/equations.