Average age

There are 20 students in the class. Several are 12 years old, and others are 13 years old. Find out how old is twelve when the average age of a class is:

a) 12.5 years

b) 12.75 years

c) 12.3 years

d) 12.35 years

Correct answer:

a =  10
b =  5
c =  14
d =  13

Step-by-step explanation:

2012⋅ a + 13⋅ (20−a)​ = 12.5  12⋅ a+13⋅ (20−a)=20⋅ 12.5  a=10  a=110​=10  a=10
12⋅ b+13⋅ (20−b)=20⋅ 12.75  b=5  b=15​=5  b=5
12⋅ c+13⋅ (20−c)=20⋅ 12.3  c=14  c=114​=14  c=14
12⋅ d+13⋅ (20−d)=20⋅ 12.35  d=13  d=113​=13  d=13

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You need to know the following knowledge to solve this word math problem:

statisticsalgebranumbersGrade of the word problem

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