Editor's Note: The following are questions received from viewers of "Mad Money," seen every day at 6 p.m. EDT on CNBC.

What do you think of 3M (MMM) - Get Report? Is this a good defensive stock?-- Chris from Philadelphia

James J. Cramer:

Since former CEO James McNerney left the company this summer for

Boeing

(BA) - Get Report

, which I own for my charitable trust,

ActionAlertsPLUS, I no longer rank 3M in the upper echelon of the manufacturing conglomerates.

I believe that viewers would be better served holding

Textron

(TXT) - Get Report

because of its aerospace exposure and discount valuation.

Is there a general rule about price-to-earnings ratios that a ratio below 10 means a stock is undervalued?-- Karl from Alabama

James J. Cramer:

The best way to compare a stock's P/E ratio is against those of other companies in the same industry, because some growth sectors, like technology, consistently demand a premium to other sectors, like the financials.

That said, you can also use the P/E ratio of a broad market index like the

S&P 500

(currently 16.5 times expected 2005 earnings) to see how a company or its industry stacks up against a wider range of companies.

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