document.write( "Question 1009551: if you combine Mary and johns ages the result is 70. Mary is 4 more than twice johns age. how old is John? \n" ); document.write( "

Algebra.Com's Answer #625025 by themasterofcircuits(27) $\"\"$ $\"About$

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This is a system of equations problem.\r
\n" ); document.write( "\n" ); document.write( "Let m=the age of Mary and j= the age of John\r
\n" ); document.write( "\n" ); document.write( "Mary's age plus John's age is 70: m+j=70 [1]\r
\n" ); document.write( "\n" ); document.write( "John's age is 4 more than 2 times Mary's age: m=2j+4 [2]\r
\n" ); document.write( "\n" ); document.write( "This is a good canidate for substitution:\r
\n" ); document.write( "\n" ); document.write( "Substitute [2] into [1]:\r
\n" ); document.write( "\n" ); document.write( "2j+4+j=70\r
\n" ); document.write( "\n" ); document.write( "=3j+4=70\r
\n" ); document.write( "\n" ); document.write( "3j=66\r
\n" ); document.write( "\n" ); document.write( "[j=22]\r
\n" ); document.write( "\n" ); document.write( "John is 22 years old\r
\n" ); document.write( "\n" ); document.write( "We could compute Mary's age by substituting 22 for j in [1], but the problem just asks for John's age, so we're finished.\r
\n" ); document.write( "\n" ); document.write( "-Aμstin \n" ); document.write( "

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