document.write( "Question 567816: the train covers 90km in uniform speed.if speed is raised 15km/hr then train covers distance in half hour less.find the original speed. \n" ); document.write( "

Algebra.Com's Answer #366739 by josmiceli(19441) $\"\"$ $\"About$

You can put this solution on YOUR website!
Let $\"+s+\"$ = original speed in km/hr
\n" ); document.write( "Let $\"+t+\"$ = time in hrs to cover $\"+90+\"$ km at speed $\"+s+\"$
\n" ); document.write( "given:
\n" ); document.write( "(1) $\"+90+=+s%2At+\"$
\n" ); document.write( "(2) $\"+90+=+%28+s+%2B+15+%29%2A%28+t+-+.5+%29+\"$
\n" ); document.write( "------------------------
\n" ); document.write( "(1) $\"+t+=+90%2Fs+\"$
\n" ); document.write( "Substitute (1) into (2)
\n" ); document.write( "(2) $\"+90+=+s%2At+%2B+15t+-+.5s+-+7.5+\"$
\n" ); document.write( "(2) $\"+90+=+s%2A%2890%2Fs%29++%2B+15%2A%2890%2Fs%29+-+.5s+-+7.5+\"$
\n" ); document.write( "(2) $\"+90+=+90+%2B+1350%2Fs+-+.5s+-+7.5+\"$
\n" ); document.write( "(2) $\"+0+=+1350%2Fs+-.5s++-+7.5+\"$
\n" ); document.write( "(2) $\"+1350%2Fs+=+.5s+%2B+7.5+\"$
\n" ); document.write( "(2) $\"+1350+=+.5s%5E2+%2B+7.5s+\"$
\n" ); document.write( "(2) $\"+5s%5E2+%2B+75s+-+13500+=+0+\"$
\n" ); document.write( "(2) $\"+s%5E2+%2B+15s+-+2700+=+0+\"$
\n" ); document.write( "Use quadratic formula
\n" ); document.write( " $\"+s+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+\"$
\n" ); document.write( " $\"+a+=+1+\"$
\n" ); document.write( " $\"+b+=+15+\"$
\n" ); document.write( " $\"+c+=+-2700+\"$
\n" ); document.write( " $\"+s+=+%28+-15+%2B-+sqrt%28+15%5E2+-+4%2A1%2A%28-2700%29+%29%29%2F%282%2A1%29+\"$
\n" ); document.write( " $\"+s+=+%28+-15+%2B-+sqrt%28+225+%2B+10800+%29%29+%2F+2+\"$
\n" ); document.write( " $\"+s+=+%28+-15+%2B-+sqrt%28+11025+%29%29+%2F+2+\"$ ( I can't use the negative square root )
\n" ); document.write( " $\"+s+=+%28+-15+%2B+105+%29+%2F+2+\"$
\n" ); document.write( " $\"+s+=+90%2F2+\"$
\n" ); document.write( " $\"+s+=+45+\"$
\n" ); document.write( "The original speed is 45 km/hr
\n" ); document.write( "check answer:
\n" ); document.write( "(1) $\"+90+=+s%2At+\"$
\n" ); document.write( "(1) $\"+90+=+45t+\"$
\n" ); document.write( "(1) $\"+t+=+2+\"$ hrs
\n" ); document.write( "and
\n" ); document.write( "(2) $\"+90+=+%28+s+%2B+15+%29%2A%28+t+-+.5+%29+\"$
\n" ); document.write( "(2) $\"+90+=+%28+45+%2B+15+%29%2A%28+2+-+.5+%29+\"$
\n" ); document.write( "(2) $\"+90+=+60%2A1.5+\"$
\n" ); document.write( "(2) $\"+90+=+90+\"$
\n" ); document.write( "OK \n" ); document.write( "

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