Correct Answer - Option 4 : 7 and 21
Given equation is,
63 ÷ 21 - 42 + 8 × 7 = 135
Interchanging numbers and applying BODMAS rule option wise,
(I) 63 ÷ 21 - 42 + 8 × 7 = 135
Interchanging 21 and 42
63 ÷ 42 - 21 + 8 × 7 = 135
1.5 - 21 + 8 × 7 = 135
1.5 - 21 + 56 = 135
1.5 - 35 = 135
-33.5 ≠ 135
(II) 63 ÷ 21 - 42 + 8 × 7 = 135
Interchanging 21 and 8
63 ÷ 8 - 42 + 21 × 7 = 135
7.875 - 42 + 21 × 7 = 135
7.875 - 42 + 147 =135
7.875 + 105 = 135
112.875 ≠ 135
(III) 63 ÷ 21 - 42 + 8 × 7 = 135
Interchanging 7 and 63
7 ÷ 21 - 42 + 8 × 63 = 135
0.33 - 42 + 8 × 63 = 135
0.33 - 42 + 504 = 135
462.33 ≠ 135
(IV) 63 ÷ 21 - 42 + 8 × 7 = 135
Interchanging 7 and 21
63 ÷ 7 - 42 + 8 × 21 = 135
9 - 42 + 8 × 21 = 135
9 - 42 + 168 = 135
9 + 126 = 135
135 = 135.
Hence, "7 and 21" is the correct answer.
In this type of questions, where the answer is a whole number,
Look for the option which will have a whole number quotient after the divide.
Like, in this question,
63 is divisible by 21 and 7 only and only one option satisfies this condition.
