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Algebra Difficulty 2.3 Junior Find the answer

The average of a,ba, b and cc is 16. The average of c,dc, d and ee is 26. The average of a,b,c,da, b, c, d, and ee is 20. What is the value of cc?

A number or a short expression. Spacing and $ signs are ignored.

Solution

Since the average of a,ba, b and cc is 16, then rac{a+b+c}{3}=16 and so a+b+c=3imes16=48a+b+c=3 imes 16=48. Since the average of c,dc, d and ee is 26, then rac{c+d+e}{3}=26 and so c+d+e=3imes26=78c+d+e=3 imes 26=78. Since the average of a,b,c,da, b, c, d, and ee is 20, then rac{a+b+c+d+e}{5}=20. Thus, a+b+c+d+e=5imes20=100a+b+c+d+e=5 imes 20=100. We note that (a+b+c)+(c+d+e)=(a+b+c+d+e)+c(a+b+c)+(c+d+e)=(a+b+c+d+e)+c and so 48+78=100+c48+78=100+c which gives c=126100=26c=126-100=26.

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