GRE数学重点考点介绍
<p> <span word="Set">Set</span></p><p> <span word="A">A</span> <span word="set">set</span> <span word="is">is</span> <span word="a">a</span> <span word="collection">collection</span> <span word="of">of</span> <span word="objects">objects</span> <span word="or">or</span> <span word="things">things</span>. <span word="Each">Each</span> <span word="object">object</span> <span word="in">in</span> <span word="a">a</span> <span word="set">set</span> <span word="a">a</span> <span word="member">member</span> <span word="or">or</span> <span word="element">element</span> <span word="of">of</span> <span word="that">that</span> <span word="set">set</span>.<span word="Size">Size</span> <span word="of">of</span> <span word="a">a</span> <span word="set">set</span> <span word="is">is</span> <span word="the">the</span> <span word="number">number</span> <span word="of">of</span> <span word="members">members</span> <span word="in">in</span> <span word="the">the</span> <span word="set">set</span>.</p><p> <span word="Example">Example</span>:</p><p> <span word="The">The</span> <span word="set">set</span> <span word="of">of</span> <span word="even">even</span> <span word="numbers">numbers</span> <span word="between">between</span> 2 <span word="and">and</span> 10 <span word="is">is</span> <span word="of">of</span> <span word="size">size</span> 5:{2,4,6,8,10}.</p><p> <span word="The">The</span> <span word="set">set</span> <span word="of">of</span> <span word="primes">primes</span> <span word="between">between</span> 2 <span word="and">and</span> 10 <span word="is">is</span> <span word="of">of</span> <span word="size">size</span> 4:{2,3,5,7}.</p><p> <span word="Remember">Remember</span>:</p><p> <span word="Each">Each</span> <span word="member">member</span> <span word="of">of</span> <span word="set">set</span> <span word="A">A</span> <span word="belongs">belongs</span> <span word="to">to</span> <span word="A">A</span> <span word="or">or</span> <span word="is">is</span> <span word="in">in</span> <span word="the">the</span> <span word="set">set</span> <span word="A">A</span>.</p><p> <span word="A">A</span> <span word="set">set</span> <span word="can">can</span> <span word="not">not</span> <span word="have">have</span> <span word="repeating">repeating</span> <span word="member">member</span>:{1,3,1,2}<span word="is">is</span> <span word="not">not</span> <span word="a">a</span> <span word="set">set</span>.</p><p> <span word="Rearranging">Rearranging</span> <span word="the">the</span> <span word="order">order</span> <span word="of">of</span> <span word="the">the</span> <span word="members">members</span> <span word="does">does</span> <span word="not">not</span> <span word="change">change</span> <span word="the">the</span> <span word="set">set</span>:{1,2,3}<span word="is">is</span> <span word="same">same</span> <span word="as">as</span>{3,2,1}.</p><p> <span word="Combinations">Combinations</span></p><p> <span word="Number">Number</span> <span word="of">of</span> <span word="ways">ways</span> <span word="we">we</span> <span word="can">can</span> <span word="select">select</span> <span word="n">n</span> <span word="objects">objects</span> <span word="from">from</span> <span word="a">a</span> <span word="group">group</span> <span word="of">of</span> <span word="m">m</span> <span word="distinct">distinct</span> <span word="objects">objects</span> <span word="is">is</span> <span word="m">m</span>!/!).</p><p> <span word="Example">Example</span>:</p><p> <span word="Number">Number</span> <span word="of">of</span> <span word="possible">possible</span> <span word="ways">ways</span> <span word="to">to</span> <span word="pick">pick</span> 4 <span word="oscar">oscar</span> <span word="nominations">nominations</span> <span word="from">from</span> <span word="a">a</span> <span word="list">list</span> <span word="of">of</span> 50 <span word="movies">movies</span> <span word="is">is</span> 50!/!)=50!/=50494847/24=230300.</p><p> <span word="Remember">Remember</span>:</p><p> <span word="This">This</span> <span word="does">does</span> <span word="not">not</span> <span word="apply">apply</span> <span word="if">if</span> <span word="there">there</span> <span word="are">are</span> <span word="identical">identical</span> <span word="objects">objects</span>.</p><p> <span word="Permutation">Permutation</span> <span word="of">of</span> <span word="Objects">Objects</span></p><p> <span word="The">The</span> <span word="number">number</span> <span word="of">of</span> <span word="ways">ways</span> <span word="n">n</span> <span word="distinct">distinct</span> <span word="objects">objects</span> <span word="can">can</span> <span word="be">be</span> <span word="ordered">ordered</span> <span word="is">is</span> <span word="n">n</span>.</p><p> <span word="Example">Example</span>:</p><p> <span word="Number">Number</span> <span word="of">of</span> <span word="ways">ways</span> 6 <span word="people">people</span> <span word="can">can</span> <span word="from">from</span> <span word="a">a</span> <span word="queue">queue</span> <span word="is">is</span> 6.</p><p> <span word="Number">Number</span> <span word="of">of</span> <span word="ways">ways</span> 5 <span word="different">different</span> <span word="cars">cars</span> <span word="can">can</span> <span word="be">be</span> <span word="parked">parked</span> <span word="in">in</span> 5 <span word="parking">parking</span> <span word="spaces">spaces</span> <span word="is">is</span> 5.</p><p> <span word="Remember">Remember</span>:</p>
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