Create an extended frequency distribution table.

To find the mean and standard deviation, we need the class midpoints ($x$), the product of frequency and midpoint ($fx$), the square of the midpoint ($x^2$), and the product of frequency and squared midpoint ($fx^2$). For the median class, we need the cumulative frequency ($cf$).

Class Interval	Frequency ($f$)	Class Midpoint ($x$)	$fx$	Cumulative Frequency ($cf$)	$x^2$	$fx^2$
64-64	5	64	320	5	4096	20480
65-69	3	67	201	8	4489	13467
70-74	6	72	432	14	5184	31104
75-79	4	77	308	18	5929	23716
80-84	8	82	656	26	6724	53792
85-89	10	87	870	36	7569	75690
90-94	1	92	92	37	8464	8464
95-99	3	97	291	40	9409	28227
Total	$\sum f = 40$		$\sum fx = 3170$			$\sum fx^2 = 254940$

The modal class is the class interval with the highest frequency.
From the table, the highest frequency is 10, which corresponds to the class interval 85-89.

The modal class is $\boxed{\text{85-89}}$.

The median class is the class where the cumulative frequency first exceeds or equals $\frac{N}{2}$.
The total number of data points is $N = \sum f = 40$.
We need to find the class containing the $\frac{N}{2}$-th value, which is the $\frac{40}{2} = 20$-th value.
Looking at the cumulative frequency ($cf$) column:

• The class 75-79 has a $cf$ of 18.
• The class 80-84 has a $cf$ of 26. Since 26 is the first cumulative frequency greater than or equal to 20, the median class is 80-84.

The median class is $\boxed{\text{80-84}}$.

The formula for the mean of grouped data is:

$$\bar{x} = \frac{\sum fx}{N}$$

Substitute the values from the table:

$$\bar{x} = \frac{3170}{40}$$ $$\bar{x} = 79.25$$

The mean is $\boxed{79.25}$.

The formula for the standard deviation of grouped data is:

$$s = \sqrt{\frac{\sum fx^2 - (\sum fx)^2 / N}{N-1}}$$

Substitute the values from the table:

$$\sum fx^2 = 254940$$ $$\sum fx = 3170$$ $$N = 40$$ $$s = \sqrt{\frac{254940 - (3170)^2 / 40}{40-1}}$$ $$s = \sqrt{\frac{254940 - 10048900 / 40}{39}}$$ $$s = \sqrt{\frac{254940 - 251222.5}{39}}$$ $$s = \sqrt{\frac{3717.5}{39}}$$ $$s = \sqrt{95.32051282}$$ $$s \approx 9.76$$

The standard deviation is $\boxed{9.76}$.