Question : Directions: By interchanging the given two signs which of the following equations will be not correct?
+ and –
I. 4 × 6 + 7 – 3 ÷ 1 = 21
II. 6 × 9 + 7 – 8 ÷ 2 = 51
Option 1: Only I
Option 2: Both I and II
Option 3: Neither I nor II
Option 4: Only II
Correct Answer: Only I
Solution :
Given:
I. 4 × 6 + 7 – 3 ÷ 1 = 21
II. 6 × 9 + 7 – 8 ÷ 2 = 51
After interchanging + and – the equations become –
First equation:
4 × 6
– 7 + 3 ÷ 1 = 21
Solving the L.H.S. of the equation –
= 4 × 6
– 7 + 3 ÷ 1
= 4 × 6
– 7 + 3
= 24 – 7 + 3
= 17 + 3 = 20
= 20
≠
21
Second equation:
6 × 9 – 7 + 8 ÷ 2 = 51
Solving the L.H.S. of the equation –
= 6 × 9 – 7 + 8 ÷ 2
= 6 × 9 – 7 + 4
= 54 – 7 + 4
= 51 = 51
⇒ L.H.S = R.H.S.
So, the first equation doesn't satisfy the R.H.S. of the equation. Hence, the first option is correct.
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