| Date | November 2018 | Marks available | 4 | Reference code | 18N.2.SL.TZ0.5 |
| Level | SL | Paper | 2 | Time zone | no time zone |
| Command term | Explain | Question number | 5 | Adapted from | N/A |
Question
The average weekly consumption for a family of four is 2700 litres of water. This includes the water needed for domestic cleaning, personal hygiene, cooking and drinking.
An online software tool is available to help families calculate how much water they are using for regular activities that require the supply of water. The software tool includes a model which estimates the water usage. A simulation can be run using this model.
The data given below estimates the amount of water (in litres) needed for different household activities:
By using the data in the table, a family uses a spreadsheet to run some simulations of how to distribute the use of water.
With reference to the scenario described above, explain the difference between a model and a simulation.
Explain how the choice of data in the table may affect the quality of the simulation.
Outline how a simulation in a spreadsheet can be organized so that the family can ensure a consumption of no more than 2700 litres per week.
The same spreadsheet is used by a group of four young people who share a house. The simulation, however, does not reflect their actual situation and the weekly target is often exceeded.
Identify two reasons why the simulation may not reflect the actual situation in this case.
Markscheme
The model is a static description of some rules;
In this case a list of appliances and their water consumption (min or max);
Whereas the simulation is the use of that model;
With input from real parameters (such as those that families may input);
Award up to [4 max].
There may be missing data:
For example, watering plants (allow any suitable example);
The consequences, e.g. the totals will be underestimated;
The data may be inaccurate;
For example, the shower times may exceed the stated;
The consequence, e.g. the results of the simulation may not be valid;
The answer shows the use of columns and rows;
The data from part (b) is included together with the addition of a TimesPerWeek variable;
Weekly total formula for each variable is included;
Overall weekly total has correct formula;TimesPerWeek is adjusted until target is met;
Award up to [2 max].
Individual and individualistic use:
They don’t know each other, and they do their laundry separately, not full load;
They don’t cook together and consume more water consequently;
Somebody washes the car every week without telling the others;
Special occasions:
Some of them may be athletes and need to wash the sport gear separately;
Somebody invites friends over night/for dinner and the water consumption increases;
Technical reasons:
There are water leaks in the house and they are not aware about them;
The counter was manipulated by the landlord years ago;
