**Notes**

Let's use sympy to make the maths easier. Let's start by making an expression that describes the curve from the chart in the previous vide.

```
import sympy as sp
g, p = sp.symbols("g, p")
exp = g * (1-p) ** g
```

You can take this expression and differentiate it with regards to `g`

.

```
sp.diff(exp, g)
```

We have a maximum value when there's a slope equal to zero. We can ask sympy to calculate this for us.

```
sp.solve(sp.diff(exp, g), g)
```

This means that we can use sympy to give us the optimal group size given a probability value.

```
g_opt = -1/sp.log(1 - p)
g_opt.subs(p, 0.01)
```

This is neat!

### Extra!

In case you're interested, we have content on sympy if you're unfamiliar.