Question : Directions: Which of the mathematical signs should be interchanged in the given equation to make it mathematically correct?
12 + 66 ÷ 11 − 4 × 91 = 159

Option 1: ÷ and ×

Option 2: + and −

Option 3: + and ×

Option 4: + and ÷

Correct Answer: + and ×

Solution : Given:
12 + 66 ÷ 11 − 4 × 91 = 159

Let's check each option –
First Option: ÷ and ×
On interchanging the mathematical signs, we get –
12 + 66 × 11 − 4 ÷ 91 = 159
On solving the L.H.S. of the equation –
= 12 + 66 × 11 − 4 ÷ 91
= 12 + 66 × 11 − 0.04
= 12 + 726 − 0.04
= 737.96 ≠ 159
Second Option: + and –
On interchanging the mathematical signs, we get –
12 – 66 ÷ 11 + 4 × 91 = 159
On solving the L.H.S. of the equation –
= 12 – 66 ÷ 11 + 4 × 91
= 12 – 6 + 4 × 91
= 12 – 6 + 364
= 370 ≠ 159
Third Option: + and ×
On interchanging the mathematical signs, we get –
12 × 66 ÷ 11 − 4 + 91 = 159
On solving the L.H.S. of the equation –
= 12 × 66 ÷ 11 − 4 + 91
= 12 × 6 − 4 + 91
= 72 − 4 + 91
= 159
Fourth Option: + and ÷
On interchanging the mathematical signs, we get –
12 ÷ 66 + 11 − 4 × 91 = 159
On solving the L.H.S. of the equation –
= 12 ÷ 66 + 11 − 4 × 91
= 0.18 + 11 − 4 × 91
= 0.18 + 11 − 364
= –352.82 ≠ 159

So, only the third option satisfies the equation. Hence, the third option is correct.