document.write( "Question 141976: At 8.15a.m, a van started from Town X heading for Town Y at a constant speed of 50km/h. Half an hour later, a lorry passed Town X also heading towards Town Y at a constant speed of 70km/h
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Algebra.Com's Answer #103383 by Edwin McCravy(20054)\"\" \"About 
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document.write( "Let t be the number of hours after 8.15am that the lorry\r\n" );
document.write( "caught up to the van.\r\n" );
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document.write( "Make this chart and put t for the van's time:\r\n" );
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document.write( "          DISTANCE        SPEED        TIME\r\n" );
document.write( "Van                                      t             \r\n" );
document.write( "Lorry        \r\n" );
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document.write( "The lorry's time at the instant the lorry caught up is one half\r\n" );
document.write( "hour less than the van's time, since it started one-half hour\r\n" );
document.write( "later.  So we put \"t-1/2\" for the time the lorry traveled before\r\n" );
document.write( "it caught up the van:\r\n" );
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document.write( "          DISTANCE        SPEED        TIME\r\n" );
document.write( "Van                                      t             \r\n" );
document.write( "Lorry                                  t-1/2 \r\n" );
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document.write( "Now we put in the speeds of 50 and 70 km/h:\r\n" );
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document.write( "          DISTANCE        SPEED        TIME\r\n" );
document.write( "Van                        50            t             \r\n" );
document.write( "Lorry                      70          t-1/2 \r\n" );
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document.write( "Now we use the formula\r\n" );
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document.write( "                  Distance = (Speed)(Time)\r\n" );
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document.write( "to fill in the two distances:\r\n" );
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document.write( "          DISTANCE        SPEED        TIME\r\n" );
document.write( "Van         50t            50            t             \r\n" );
document.write( "Lorry     70(t-1/2)        70          t-1/2 \r\n" );
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document.write( "The two distances were equal at the instant when the \r\n" );
document.write( "lorry caught up.  So\r\n" );
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document.write( "    50t = 70(t-1/2)\r\n" );
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document.write( "Can you solve that for t?\r\n" );
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document.write( "Answer: t = 1 3/4 hours.\r\n" );
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document.write( "That is, an hour and 45 minutes after 8.15am, \r\n" );
document.write( "which would be 10.00am.\r\n" );
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document.write( "---------------------\r\n" );
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document.write( "(b) If the lorry reached Town Y at 1.45pm, what \r\n" );
document.write( "is the distance between the 2 towns?\r\n" );
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document.write( "Let d = the distance between the 2 towns.\r\n" );
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document.write( "The lorry started at 8.45am (one half hour after 8.15am) \r\n" );
document.write( "and reached town Y at 1.45pm.  That is 5 hours.  The \r\n" );
document.write( "speed of the lorry was 70 km/hr.\r\n" );
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document.write( "  Use distance = speed times time.\r\n" );
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document.write( "             d = 70(5)\r\n" );
document.write( "             d = 350 km.\r\n" );
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document.write( "Edwin

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