求助！！！标准方差和小数的题

joba

q1:a certain list of 100 data has a average 6 and a standard deviation of d,where d is positive ,which of the following paris of data, when added to the list ,must result in a list  of 102 data with standard deviation less than d?

q2: 9.4   9.9   9.9  9.9 10.0  10.2  10.2  10.5
the number and the standard deviation of the 8 numbers shown are 10 and 0.3 ,respectively,what percent of the 8 numbers are within 1 standard deviation of the mean?

q3S:  IS THE hundredths digit of the decimal d greater than 5?
        1)the tenths digit of 10d is 7
         2)the thousandths digit of d/10 is 7

两道关于标准方差？的题，还有一道小数的题，
这种题总是不会做，
大家能讲讲这种题怎么做吗?

maximeason

q3答案是什么？D吗？

shirleyon

q3主要是对题目的理解
Tens 十位 　　Tenths 十分位
也就是说，　　Tenths 是指小数点后第一位
hundredths ，thousandths 也是指小数点后的。