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The average of Kanchan's marks in 7 subjects is 75. Her average in six subjects excluding Science is 72. How many marks did she get in Science?
90
93
95
72
93
Calculate the difference: Science marks = (7 ×75)−(6×72)=525−432=93.Alternatively: 75 + 6 ×(75−72)=75+6×3=75+18=93.
Average marks in 7 subjects = 75. Average marks in 6 subjects (excluding Science) = 72.
Total=Average×n
Calculate the difference: Science marks = (7 ×75)−(6×72)=525−432=93.Alternatively: 75 + 6 ×(75−72)=75+6×3=75+18=93.
Students often multiply by 6 when they should be multiplying by 7 or vice versa, or forget the difference in the number of subjects.
Calculate total marks for 7 subjects
To find the sum of all 7 subjects, multiply the average by the number of subjects.
7×75=525
Calculate total marks for 6 subjects
To find the sum of the 6 subjects excluding Science, multiply the given average by 6.
6×72=432
Find marks in Science
The difference between the total of 7 subjects and the total of 6 subjects gives the marks in Science.
525−432=93
B is correct because the calculated value of Science marks is 93.
This type of 'missing item' problem is common in average-based statistics. Always remember that Total = Average * Count; it is the most reliable way to avoid errors.
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