A test marked out of 100 is written by 800 studnets. The cumulative frequency graph for the marks is given below.
http://i42.tinypic.com/oge007.png
(a) Write down the number of students who scored 40 marks or less on the test.
(b) The middle 50% of test results lie between marks a and b, where a < b. Find a and b.
http://i42.tinypic.com/oge007.png
(a) Write down the number of students who scored 40 marks or less on the test.
(b) The middle 50% of test results lie between marks a and b, where a < b. Find a and b.
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a) Go across to 40 on the horizontal scale, up to the curve and across to the vertical scale to see that 100 students scored 40 marks or less.
b) The middle 50% is between 25% and 75%, ie. the upper and lower quartiles.
25% of 800 is 200. Read across from 200 students and down to see the mark is 55.
75% of 800 is 600. Read across from 600 students and down to see the mark is 75.
So the marks lie between a = 55 and b = 75.
b) The middle 50% is between 25% and 75%, ie. the upper and lower quartiles.
25% of 800 is 200. Read across from 200 students and down to see the mark is 55.
75% of 800 is 600. Read across from 600 students and down to see the mark is 75.
So the marks lie between a = 55 and b = 75.