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## Problem Solving

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**Problem Solving**Standard Grade Biology**4th Year Supported Study**• Your prelim will involve both Knowledge and Understanding (KU) – the Biology facts AND Problem Solving (PS) – the Maths side of the course. • Problem Solving Skills include graphs (bar and line), averages, ratios, percentage increases, percentage decreases, pie charts, questions about a passage, etc.**Problem Solving Questions**• The answer is usually in the data or information provided, all you have to do is find it • Alternatively you may need to calculate the answer from the data given e.g. ratios and percentages • You may have to draw a line graph, bar chart or pie chart • READ THE QUESTIONS CAREFULLY!**Percent means per hundred or for every hundred**To calculate a percentage Create a fraction and multiply by 100 e.g. In a class of 24 pupils 14 are boys, what is the % of girls in the class? ANSWER If 14 of the pupils are boys, 10 of the pupils are girls Express this as a fraction Convert to a % by multiplying by 100 Percentage of girls in the class is 10/24 X 100 = ? Working With Percentages**You can be asked to calculate a percentage increase or**decrease ChangeX 100 Original e.g. a piece of carrot of mass 10g is placed in salt solution for 2 hours and then reweighed. Its new mass is 9.4g, calculate the % decrease in mass. ANSWER Change in mass = 0.6g Original mass =10g % decrease = 0.6 x 100 10 = 6% % Increase and Decrease**Cont.**• You may be asked to calculate a % of a number e.g. What is 40% of 200? 40 X 200 = 80 100**A ratio compares two or more quantities in a particular**order Your answer must contain only whole numbers e.g. A class of 25 pupils contains 15 boys , calculate the ratio of girls to boys in the class. ANSWER Number of girls = 10 Number of boys =15 Ratio of girls to boys is 10:15 Both 10 and 15 can be divided by 5 Ratio of girls to boys is 2:3 There is no number that can divide both 2 and 3 without giving a fraction so the answer is left as 2:3 Ratios**You may be asked to calculate an average**What is average of these numbers? 23, 45, 28,32 ANSWER 23+45+28+32 = 128 Divide by 4 Answer = 31 Averages**Control Experiments**• A control is an experiment where every thing is kept the same except for one factor • This is usually the factor that is thought to cause the effect we are observing • We can substitute a liquid with distilled water • Dead tissue or glass beads for living tissue • A control makes an experiment FAIR**Reliable Results**To make results reliable we can do several things • Repeat the experiment several times and calculate an average of the results • Get data from other students and calculate an average of the results**Drawing Line Graphs**• You may be given a table of results and be asked to use them to draw a line graph • Use the table headings to label the axes • The factor that the experimenter controlled is always put on the x-axis • The factor that is measured in the experiment is put on the y-axis • Sometimes one of the axes is already labelled for you**Plotting a Line Graph**• Choose a simple scale going up in multiples of 1, 2, 5, 10, 20, 50, 100 etc • Make sure that the scale you have chosen means that you will use more than half the grid given • Never choose an awkward scale like each square going up in multiples of 3 or 7 • Plot each point using a sharp pencil and mark with an X • Join the points using a ruler • Do not join to 0,0 unless it is in the table**Bar Charts**• Chose a suitable scale as for line graphs • All the bars must be the same width • Do not waste time colouring in the bars • If you want to make them more visible , cross hatch them neatly