Define [a,b,c] to mean (a+b)/(c), where c≠0. What is the value of [[60,30,90],[2,1,3],[10,5,15]]?

1998 AMC 12 Problem 4

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Define

[a,b,c]

to mean

\frac{a+b}{c},

where

c\ne0.

What is the value of

[[60,30,90],[2,1,3],[10,5,15]]?

0

0.5

1

1.5

2

Evaluate each of the three inner brackets first

All three inner brackets have the same value

Each inner value is

1:

\frac{90}{90}=1,\frac{3}{3}=1,

and

\frac{15}{15}=1.

Thus the outer expression is

[1,1,1]=\frac{1+1}{1}=2.

The correct answer is E.