Question

Which two signs or numbers need to be interchanged to make the following equation correct?

(21 ÷ 3) × 9 + 3 = 10

1. × and ÷
2. ÷ and +
3. 9 and 21
4. 9 and 10 

Answer 1

Correct Answer - Option 1 : × and ÷

Given equation: (21 ÷ 3) × 9 + 3 = 10

Using options:

Option 1)

After interchanging ‘× and ÷’ we get:

L.H.S. of equation: (21 × 3) ÷ 9 + 3 

→  63 ÷ 9 + 3 

→ 7 + 3 

→ 10 = RHS

Option 2)

After interchanging ‘÷ and +’ we get:

L.H.S. of equation: (21+3) × 9 ÷ 3 

→  24 × 9 ÷ 3  

→ 24 × 3 

→ 72 ≠ RHS

Option 3)

After interchanging ‘9 and 21’ we get:

L.H.S. of equation: (9 ÷ 3) × 21 + 3 = 10

→  3 × 21 + 3  

→ 63 + 3

→ 66 ≠ RHS

Option 4)

After interchanging ‘9 and 10’ we get:

L.H.S. of equation: (21 ÷ 3) × 10 + 3 = 9

→  7× 10 + 3  

→ 70 + 3

→ 73 ≠ 9 RHS

Hence, the correct answer is ‘× and ÷’.