Answer:
This assumes the question should read:
"The average of 5 girls is 16 [not 6] yrs. the average of 4 of them is 16½. what is d age of d fifth gal
The age, d, is 14 years.
Step-by-step explanation:
When the girl with age d is not included, the average goes up to 16.5 years. Let's define GroupA as the sum of the ages of the 4 girls whose average age is 16.5 years. d is the age of the girl that is removed from the average.
We know that all the girls (GroupA + d) have an average age of 16 years:
(GroupA + d)/5 = 16 years [Add the ages for all the girls (GroupA and d) and divide by 5 to obtain the average age for the larger group].
We know that when d is removed, the average for the 4 remaining girls (GroupA) is 16.5 years:
(GroupA)/4 = 16.5 years
This tells us the sum of the ages for GroupA:
GroupA = 4*(16.5)
GroupA total = 66 years
From above: (GroupA + d)/5 = 16 years
Since GroupA = 66 years, (66 years + d)/5 = 16 years
(66 years + d) = 90 years
d = 14 years
