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英数第一周周二1.Threepipescanbeusedtofillatank.Itisfilledin10hoursusingonlythefirstpipe,in12hoursusingonlythesecondpipeandin15hoursusingonlythethirdone.Apressureproblemcutstheflowcapacityofeachpipeinhalf.Itisthendecidedtousethethreepipestogether.Howlongwillittaketofillthetank?2.Howmanyintegersbetween1and1000(inclusive)donotcontainthedigits8or9?3.Mr.Martinboughttwoballswhichhethenresoldat$1.20each.Basedonthecostoftheballs(thepricehepaid),Mr.Martinmadeaprofitof20%ononeoftheballsandencounteredalossof20%ontheother.Overall,bothsaleshaveledtoA.nonetprofitB.alossof4centsC.aprofitof4centsD.alossof10cents4.Rainsfallsallnightoveralake.Thetotalrainfallis50litrespersquaremeter.Byhowmuchdoesthesurfaceofthelakerise?5.A,BandCarethreenumbers.IfC-2A=50andB+3A=10,thentheaverageofthethreenumbersis6.Youmakeapurchaseandpaywithcoins.Ifyougivethesalesclerkthesmallestnumberofcoinspossible,whichofthefollowingamountswouldrequirethemostcoinstopayfor?A.24B.44C.48D.67E.967.Howmanywayscanthevalue13beexpressedasthesumofexactly3differentpositiveintegers?Forexample,13=1+4+8isonesuchway.Notethat13=4+8+1doesnotcountasa“different”waysincethesameintegersareinvolvedinthesum.A.5B.6C.7D.8E.148.IfAis10%ofC,andBis25%ofC,whatpercentsofBisA?答案：1.8hours2.5123.D4.0.5m5.206.B7.D8.40