Here's a table of missions to Mars

I count 30 total missions (including Mars Odyssey as a success, which may be premature), with the US successful 9 out of 14 attempts and the Soviets successful 6 out of 16, and that's being generous - I don't think the Soviets have had an unqualifiedly successful Mars mission.

I didn't count Nozomi.

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Everything I need to know I learned through Googling.