By interchanging the given two signs which of the following equation will be NOT correct? + and − I. 18 ÷ 3 + 8 × 5 − 4 = 20 II. 6 + 8 × 9 ÷ 3 − 4 = 14

Correct — B.
Rule: swap + and − in each equation, then evaluate with BODMAS.

I: 18 ÷ 3 − 8 × 5 + 4
= 6 − 40 + 4
= −30, not 20 ✗

II: 6 − 8 × 9 ÷ 3 + 4
= 6 − 24 + 4
= −14, not 14 ✗

Both are NOT correct → option (b).

Why the others are wrong

• (a)
  Neither I nor II — Neither I nor II would mean both equations hold after the swap. I comes to −30 and II to −14, so both fail.
• (c)
  Only II — Only II leaves out I. After the swap I gives 6 − 40 + 4 = −30, far from 20, so it fails too.
• (d)
  Only I — Only I treats II as correct. II gives −14, not 14; dropping the minus sign is what makes it look right.

This item asks which equations become NOT correct after swapping + and −. Rewrite each equation with the signs exchanged, evaluate with BODMAS, and compare with the printed right side.

The negative wording is the main hazard. Here 'Neither I nor II' means both equations hold, and 'Both I and II' means both fail.

Key facts

• BODMAS: × and ÷ left to right before + and −.
• 8 × 9 ÷ 3 = 72 ÷ 3 = 24.
• −14 and 14 are different values: the sign is part of the result.

Common traps

• Dropping the minus in −14 and passing II as correct
• Reading Neither I nor II as neither is correct, when the question asks which are NOT correct

No directly related past PYQ was found.