6769
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2011-02-01T00:00:01
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<p>In Emily's first spelling test of this new term she scored one mark out of five, so she decided to work really hard to improve her scores. Assuming that she succeeds on scoring full marks in all her tests after the first, how many more tests does she need to take to increase her average to more than $80$%.<br></br>
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If you liked this problem, <a href="http://nrich.maths.org/public/viewer.php?obj_id=1118&part=">here is an NRICH task</a> which challenges you to use similar mathematical ideas.</p>
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After her second test her average mark is $\frac{6}{10}$, after her
third test her average is $\frac{11}{15}$, after her fourth it is
$\frac{16}{20}=\frac{4}{5}=80$% exactly and after the fifth it is
$\frac{21}{25}=84$%. <br></br>
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So she needs to take four more tests to obtain an average mark of
more than $80$%.<br></br></mdoxml>
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Weekly Problem 12 - 2010
Fractions, Decimals, Percentages, Ratio and Proportion
Percentages
Handling, Processing and Representing Data
Averages