The average marks of 14 students was 71.
This mean : ( x1 + x2 + x3 + ... x14 ) / 14 = 71
( x1 + x2 + x3 + ... x14 ) / 14 = 71 Multiply both sides by 14
x1 + x2 + x3 + ... x14 = 71 * 14
x1 + x2 + x3 + ... x14 = 994 = Total marks
On this marks you must add 56 - 42 = 14 and subtract 74 - 32 = 42
New marks = 994 + 14 - 42 = 966
The correct average = 966 / 14 = 69
Average age of seven persons in a group is 30 years.
This mean : ( x1 + x2 + x3 + x4 + x5 + x6 + x7 ) / 7 = 30
( x1 + x2 + x3 + x4 + x5 + x6 + x7 ) / 7 = 30 Multiply both sides by 7
x1 + x2 + x3 + x4 + x5 + x6 + x7 = 30 * 7
x1 + x2 + x3 + x4 + x5 + x6 + x7 = 210
The average age of five persons of this group is 31 years.
This mean : ( x1 + x2 + x3 + x4 + x5 ) / 5 = 31
( x1 + x2 + x3 + x4 + x5 ) / 5 = 31 Multiply both sides by 5
x1 + x2 + x3 + x4 + x5 = 31 * 5
x1 + x2 + x3 + x4 + x5 = 155
Sum of the age of other two persons = ( x1 + x2 + x3 + x4 + x5 + x6 + x7 ) - ( x1 + x2 + x3 + x4 + x5 ) = x6 + x7 = 210 - 155 = 55
The average age of the other two persons = 55 / 2 = 27.5 years
The average marks of 14 students was 71. It was later found that the marks of one of the students has been wrongly entered as 42 instead of 56 and of another as 74 instead of 32. What is the correct average?
Average age of seven persons in a group is 30 years, the average age of five persons of this group is 31 years. What is the average age of the other two persons in the group?
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