If 'a' means 'plus', 'b' means 'minus', 'c' means 'multiplied by', and 'd' means 'divided by', then evaluate the following expression: 16 c 12 b 6 d 2 a 17 = ?

If '+' is interchanged with '-' and '×' is interchanged with '÷', what will come in place of '?' in the following equation? 529 ÷ 23 + 89 - 12 × 9 = ?

By interchanging which two signs will the given equation become correct? 15 - 9 ÷ 6 × 10 + 5 = 25