Help 7 ​

50, 46, 54, 51, 29, 52, 48, 54, 47, 48

Mean  = 47.9

Std Dev = 6.8

So....1 std dev   from the mean lies between

47.9 - 6.8    and 47.9 + 6.8   = 

41.1     and    54.7

There are 9 scores falling within this range  = 90% of the data

We expect 68%

So...."D"  is correct