One goes like this

σ=

**√**(ΣfXm^2)/n - X^2

And the other like this

S.D =

**√**NΣfXm^2 - (ΣfXm)^2 / N(N-1)

There is a table we have to solve for standard deviation

Interval | f | Xm | fXm | Xm^2 | fXm^2 |

41-50 | 14 | 45.5 | 773.3 | 2070.25 | 28,983.5 |

31-40 | 25 | 35.5 | 887.5 | 1260.25 | 31,506. 25 |

21-30 | 24 | 25.5 | 612 | 650.25 | 15,606 |

11-20 | 16 | 15.5 | 248 | 240.25 | 3,844 |

1-10 | 6 | 5.5 | 33 | 30.25 | 181.5 |

N=88 ΣfXm= 2553.8 ΣfXm^2= 80,121.25

First formula solution

80,121.25 / 88 = 910.46875

910.46875 - 842.3186983471074 = 68.15

Second formula solution

80,121.5 * 88 = 7,050,670

2553.8 ^2= 6,521,894.44

7,050,670 - 6521,894.44 = 528,775.56

528,775.56 / 7656 = 69.06

Why are the two solutions different? Is there something wrong?