document.write( "Question 517531: Mary is 3 years older than her brother Tom, and Tom is 4 years older than John. Three years ago Mary was twice as old as John. How old is each now? \n" ); document.write( "
Algebra.Com's Answer #344834 by Maths68(1474)![]() ![]() You can put this solution on YOUR website! Let \n" ); document.write( "Present age of Tom = t \n" ); document.write( "Present age of John = j \n" ); document.write( "Present age of Mary =m\r \n" ); document.write( "\n" ); document.write( "Mary is 3 years older than her brother Tom \n" ); document.write( "m=t+3............(1) \n" ); document.write( "Tom is 4 years older than John \n" ); document.write( "t=j+4.............(2) \n" ); document.write( "Three years ago Mary's age was (m-3) and John was (j-3) \n" ); document.write( "Then Mary was twice as old as John \n" ); document.write( "m-3=2(j-3) \n" ); document.write( "m-3=2j-6 \n" ); document.write( "m=2j-6+3 \n" ); document.write( "m=2j-3.............(3)\r \n" ); document.write( "\n" ); document.write( "We have three equations and three unknowns (m,t,j) and we can solve these equation either by substitution method or elimination method \n" ); document.write( "m=t+3............(1) \n" ); document.write( "t=j+4.............(2) \n" ); document.write( "m=2j-3.............(3)\r \n" ); document.write( "\n" ); document.write( "Put the value of m from (1) to (3) \n" ); document.write( "t+3=2j-3 \n" ); document.write( "t=2j-3-3 \n" ); document.write( "t=2j-6...............(4) \n" ); document.write( "Put the value of t from (2) to (4) \n" ); document.write( "j+4=2j-6 \n" ); document.write( "j-2j=-6-4 \n" ); document.write( "-j=-10 \n" ); document.write( "Multiply by -1 both sides of above equation \n" ); document.write( "j=10 \n" ); document.write( "Put the value of j in (2) \n" ); document.write( "t=j+4 \n" ); document.write( "t=10+4 \n" ); document.write( "t=14 \n" ); document.write( "Put the value of t in (1) \n" ); document.write( "m=t+3............(1) \n" ); document.write( "m=14+3 \n" ); document.write( "m=17\r \n" ); document.write( " \n" ); document.write( " \n" ); document.write( "\n" ); document.write( "Present age of Tom = t = 14 years old \n" ); document.write( "Present age of John = j = 10 years old \n" ); document.write( "Present age of Mary =m = 17 years old\r \n" ); document.write( "\n" ); document.write( " \n" ); document.write( " |