find the sum of 18 numbers whose mean is 21
Answers
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We know, the mean of a set of numerical values, is calculated by adding them together and dividing by the number of terms in the set.
1st method
Accordingly the equation is:
Mean = sum of numbers / number of terms
Sum of numbers = number of terms × mean
Mean of 20 nos.= 18
THerefore, sum of 20 nos.= 20 × 18 = 360
When 2 is added to each of the numbers, we get
360 + (20 × 2)
360 + 40
= 400
Now, new mean value of 20 nos.= 400 / 20
= 20
Answer new mean value after addition of 2 to each number will be 20
2nd method
In mathematics, the mean will also increase / reduced by the same quantity, if similar quantity is increased / reduced from each terms.
Therefore New mean = earlier mean + increase in terms
= 18 + 2
= 20
New mean will be 20
Answer new mean value after substraction of 4 from each number will be 20