High School Maths Examples and Questions

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Answers − Solving Equations, Addition and Subtraction 1

1.   If 20 + y = 42, solve y

  The inverse of 20 is − 20. So subtract 20 from both sides

  
  20+y= 42
20  =20
  
  
          y=  22

  To verify, put the value of y = 22 back into the original equation
   20 + 22 = 42

2.   If 6 + z = 15, solve z

  The inverse of 6 is − 6. So subtract 6 from both sides

  
  6+z= 15
6  =6
  
  
       z=    9

  To check, put the value of z = 9 back into the original equation
   6 + 9 = 15

3.   If 7 + t = 35, what is value of t?

  The inverse of 7 is − 7. So subtract 7 from both sides

  
  7+t= 35
7  =7
  
  
       t=   28

  To verify, put the value of t = 28 back into the original equation
   7 + 28 = 35

4.   If 9 + z = 7, solve z

  The inverse of 9 is − 9. So subtract 9 from both sides

  
  9+z= 7
9  =9
  
  
        z=−2

  To check, put the value of z = −2 back into the original equation
   9 + (−2) = 9 − 2 = 7

5.   If x − 15 = 7, what is value of x?

  The inverse of − 15 is + 15. So add 15 to both sides

  
  x15= 7
   +15=+15
  
  
   x       =   22

  To verify, put the value of x = 22 back into the original equation
   22 − 15 = 7

6.   If y − 120 = 4, solve y

  The inverse of − 120 is + 120. So add 120 to both sides

  
  y120= 4
   +120=+120
  
  
   y        =  124

  To check, put the value of y = 120 back into the original equation
   124 − 120 = 4

7.   If z − 10 = −5, what is value of z?

  The inverse of − 10 is + 10. So add 10 to both sides

  
  z10=5
   +10=+10
  
  
   z      =    5

  To verify, put the value of z = 5 back into the original equation
   5 − 10 = −5

8.   If a − 25 = −38, solve a

  The inverse of − 25 is + 25. So add 25 to both sides

  
  a25=38
   +25=+25
  
  
   a      =13

  To check, put the value of a = −13 back into the original equation
   −13 − 25 = −38

9.   If 17 + b = −5, what is value of b?

  The inverse of 17 is − 17. So subtract 17 from both sides

  
  17+b=5
17  =17
  
  
         b=−22

  To verify, put the value of b = − 22 back into the original equation
   17 + ( − 22 ) = 17 − 22 = −5

10.   If c + 20 = −34, solve c

  The inverse of 20 is − 20. So subtract 20 from both sides

  
  c+20=−34
  20=−20
  
  
         c=−54

  To check, put the value of c = −54 back into the original equation
   −54 + 20 = −34


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