Question

Which two signs on the LHS need to be interchanged to correct the equation: $16+1-3\times 2=21?$

• A. - and +
• B. + and x
• C. x and -
• D. None of the above

Answer 1

The correct option is A - and +

Given equation is 16 + 1 - 3 x 2 = 21

Interchange - and +

16 - 1 + 3 x 2
= 16 - 1 + 6
= 16 + 6 - 1
= 22 - 1
= 21

Try interchanging + and x
16 x 1 - 3 + 2
= 16 - 3 + 2
= 16 - 1
= 15
The equation turns out to be wrong.

Interchanging x and -
16 + 1 x 3 - 2
= 16 + 3 - 2
= 19 - 2
= 17
The equation turns out to be wrong with this interchange.

So, $16-1+3\times 2=21$ is the correct equation.