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Algebra/Cross products of proportions

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Question
Hi I would like to know how to solve the following:

         2.2/3.3=a-2/a-1

        Any help on this would be great , thanks.

Answer
Hello Suzi,

It is a bit ambiguous, since it is not clear if you meant
1. 2.2/3.3=a-2/a-1, or
2. 2.2/3.3=(a-2)/(a-1)

They are quite different!  I'll assume you meant (2), since the subject you indicated is
"cross product of proportions."

First, to simplify the problem, I would simplify 2.2/3.3 to 2/3.
So, this gives: 2/3=(a-2)/(a-1), now "cross multiply" to get:
2(a-1)=3(a-2) ==> 2a-2=3a-6, now subtract 2a from both sides to get: -2=a-6,
then add 6 to both sides: 4=a...so a=4.

Good?

Abe

Algebra

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Abe Mantell

Expertise

Hello, I am a college professor of mathematics and regularly teach all levels from elementary mathematics through differential equations, and would be happy to assist anyone with such questions!

Experience

Over 15 years teaching at the college level.

Organizations
NCTM, NYSMATYC, AMATYC, MAA, NYSUT, AFT.

Education/Credentials
B.S. in Mathematics from Rensselaer Polytechnic Institute
M.S. (and A.B.D.) in Applied Mathematics from SUNY @ Stony Brook

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