Q1. After interchanging + and – as well as 8 and 7, which one of the following equations becomes correct?
A 8 – 7 + 3 × 5 = 35
B 7 × 8 + 6 – 9 = 25
C 6 + 8 × 2 – 7 = 0 Correct
D 8 × 2 + 7 – 6 = 9
Explanation
Apply both interchanges together: every + becomes –, every – becomes +, every 8 becomes 7, and every 7 becomes 8. The expression 6 + 8 × 2 – 7 = 0 changes to 6 – 7 × 2 + 8 = 0. Using the usual order of operations, this is 6 – 14 + 8 = 0, so it is correct. The expression beginning with 8 – 7 becomes 7 + 8 – 3 × 5, which is 0, not 35. The expression 7 × 8 + 6 – 9 and the one 8 × 2 + 7 – 6 also do not match their right-hand sides after the swaps.