Amixture of four gases exerts a total pressure of 860 mm hg. gases a and b each exert 220 mm hg. gas c exerts 110 mm hg. what pressure is exerted by gas d?

An equation that is very useful for this type of problem is called the partial sum, where all of the types of (whatever) equals to a certain amount of measurement based on a question. So in this case, an example would be "Total Pressure = Gas A + Gas B + Gas C + Gas D. Now substitute everything in, 860 mm Hg = 220 mm Hg + 220 mm Hg + 110 mm Hg + Gas D, leaving Gas D left to solve. Simplify it into 860 mm Hg = 550 mm Hg + Gas D, minus the 550 on both sides. This will now be 310 mm Hg = Gas D. So, the answer would be 310 mm Hg.

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