### Epidemic Modelling

Use the computer to model an epidemic. Try out public health policies to control the spread of the epidemic, to minimise the number of sick days and deaths.

### bioNRICH

bioNRICH is the area of the stemNRICH site devoted to the mathematics underlying the study of the biological sciences, designed to help develop the mathematics required to get the most from your study of biology at A-level and university.

### Conversion Sorter

Can you break down this conversion process into logical steps?

# Mixed up Mixture

##### Stage: 4 Challenge Level:

First divide the numbers into groups according to whether they are concentrations, pure numbers, or volumes.

Secondly, group the concentrations into pairs, along with the required dilution factor. Then, divide 5ml by the dilution factor to additionally find the volume added.

The numbers should be in groups of 4 now, with three additional outlying numbers.

Thirdly, think which of the components added would be measured as a number per ml, rather than a number of moles per ml. This will assign one group of 4 numbers.

Fourthly, think which of the remaining items has a large molecular weight, and so will only have a low molar concentration added. Assign this group of 4 numbers.

The final two groups are hard to assign: research what the intracellular concentration of sodium ions is, since the NaCl is added to keep the solution isotonic.

The data should be all assigned now, and the sum of the added volumes should be equal to one of the leftover numbers. What might the final number represent?