What will come in place of '?' in the following equation, if '+' and '–' are interchanged and also '×' and '÷' are interchanged? 20 × 5 − 10 + 5 ÷ 2 = ?

If: 'A % B' means 'A is multiplied by B', 'A # B' means 'A is added to B', 'A @ B' means 'A is divided by B', and 'A $ B' means 'B is subtracted from A'; then what is the value of 15 @ 5 % 7 # 9 $ 4?

Which two numbers should be interchanged to make the given equation correct? 98 ÷ 3 + 25 × 7 - 18 = 71