Which two signs should be interchanged to make the given equation correct?
646 ÷ 19 – 746 + 20 × 34 = 100
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → ‘–’ and ‘+’
Interchange the two signs of an option and work out the left side by BODMAS; the right option makes it 100.
Interchanging – and + gives 646 ÷ 19 + 746 – 20 × 34
\(646\div19=34\)
\(20\times34=680\)
\(34+746-680=100\), which equals the right side
Why the other options are incorrect
Option (1) ‘–’ and ‘×’ — Incorrect. 646 ÷ 19 × 746 + 20 – 34 \(=25364+20-34=\) 25350, not 100.
Option (2) ‘×’ and ‘+’ — Incorrect. 646 ÷ 19 – 746 × 20 + 34 \(=34-14920+34=\) –14852, not 100.
Option (4) ‘×’ and ‘÷’ — Incorrect. 646 × 19 – 746 + 20 ÷ 34 \(\displaystyle =12274-746+\frac{10}{17}\), about 11528.6, not 100.