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WAEC Mathematics 2010 Question 43

Question 43

Number Bases

The subtraction below is in base seven. Find the missing number.
5162 − 2644 = 2*15

  1. A.2
  2. B.3
  3. C.4
  4. D.5
Show the answer and explanation

Answer: A (2)

Explanation

In base seven: 2 − 4 needs a borrow: 9 − 4 = 5; then 5 − 4 = 1; then 1 − 6 needs a borrow: 8 − 6 = 2; then 4 − 2 = 2. So 5162 − 2644 = 2215 and the missing digit is 2.