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answer is 420.
The SD distribution can be represented as 2%(3rd sd),14%(2ndsd),34%(1st sd) on each side of the mean.
Since the mean is 10, and 68% i.e 34%+34% of the dist lies within sd=2, so the 1st sd=2
So the percentage of records which are less than 12 will be
2+14+34+34= 84%.
84% of 500=420.
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