Question : Directions: Select the option related to the sixth number in the same way as the first number is related to the second number and the third number is related to the fourth number.
12 : 132 :: 8 : 56 :: ? : 20
Option 1: 5
Option 2: 6
Option 3: 7
Option 4: 4
Correct Answer: 5
Solution :
Given:
12 : 132 :: 8 : 56 :: ? : 20
Subtract 1 from the first number, and then multiply the resultant with the first number, to get the second number in each number pair –
Like, 12 : 132→12 × (12 – 1) = 12 × 11 = 132
And, 8 : 56→8 × (8 – 1) = 8 × 7 = 56
Similarly, follow the same pattern for ? : 20→
⇒ a × (a – 1) = 20
⇒ a
2
– a = 20
⇒ a
2
– a – 20 = 0
⇒ a = 5 and a = –4
So, 5 is the required missing number. Hence, the first option is correct.
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