GK 2019 Q2
2. The expression 2 − 0 − 1 − 9 contains four digits and three minus signs. What is the largest value that can be obtained by inserting exactly one pair of brackets into the expression?
- A 13
- B 12
- C 10
- D 9
- E 8
Grey Kangaroo 2019, Question 2. © UK Mathematics Trust. Original paper on ukmt.org.uk
Answer: B 12
Since 2 + 0 + 1 + 9 = 12 and by inserting brackets only + or − signs are possible between the numbers, no value greater than 12 may be obtained. Also, 2 − (0 − 1 − 9) = 2 − 0 + 1 + 9 = 12 and hence a result of 12 is possible. Therefore the largest possible value that can be obtained is 12.
Solution © UK Mathematics Trust, from the GK 2019 solutions.