adding weights to workout routine

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I have currently been doing Zumba for a year now and have lost about 40 lbs, but have been on this darn plateau for over 2 months now. Nothing! Not one pound lost! I have been told if you add strength training to your workout, you can burn more and start toning and sculpting. The problem is, I don't know where to start and personal trainers are sooooo expensive! What should I do? Any advice?