NCERT Exemplar Solutions
Class 6 - Mathematics - Unit 7: Algebra - Problems and Solutions
Question 88

Question. 88

If m is a whole number less than 5, complete the table and by inspection of the table, find the solution of the equation 2m − 5 = −1 :

m01234
2m−5−5−3−113

Answer:

Solution is m = 2

Detailed Answer with Explanation:

Goal: We want to find the value of m (a whole number less than 5) that makes the equation true:

Left side: (2m - 5)
Right side: (-1)

Meaning: A “solution” is the value of (m) for which the left side becomes exactly (-1).

Given table

(m) 0 1 2 3 4
(2m - 5) (-5) (-3) (-1) (1) (3)

Check each value of (m) (by inspection)

  1. For (m = 0):
    Compute (2m): (2 imes 0 = 0)
    Now (2m - 5): (0 - 5 = -5)
    Compare with (-1): (-5 eq -1) → Not a solution.
  2. For (m = 1):
    Compute (2m): (2 imes 1 = 2)
    Now (2m - 5): (2 - 5 = -3)
    Compare with (-1): (-3 eq -1) → Not a solution.
  3. For (m = 2):
    Compute (2m): (2 imes 2 = 4)
    Now (2m - 5): (4 - 5 = -1)
    Compare with (-1): (-1 = -1) → This matches!
  4. For (m = 3):
    Compute (2m): (2 imes 3 = 6)
    Now (2m - 5): (6 - 5 = 1)
    Compare with (-1): (1 eq -1) → Not a solution.
  5. For (m = 4):
    Compute (2m): (2 imes 4 = 8)
    Now (2m - 5): (8 - 5 = 3)
    Compare with (-1): (3 eq -1) → Not a solution.

Conclusion

The only value that makes the left side equal to the right side is:

Solution: (m = 2)

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