The logic followed here is : [(1st number × 2) + 2nd number] ÷ 10 = 3rd number
Given :
(10, 20, 4)
[(10 × 2) + 20] ÷ 10 = 4
[20 + 20] ÷ 10 = 4
40 ÷ 10 = 4
4 = 4 (LHS = RHS)
And,
(15, 30, 6)
[(15 × 2) + 30] ÷ 10 = 6
[30 + 30] ÷ 10 = 6
60 ÷ 10 = 6
6 = 6 (LHS = RHS)
So,
Option - (1) : (20, 40, 8)
[(20 × 2) + 40] ÷ 10 = 8
[40 + 40] ÷ 10 = 8
80 ÷ 10 = 8
8 = 8 (LHS = RHS)
Option - (2) : (20, 30, 8)
[(20 × 2) + 30] ÷ 10 = 6
[40 + 30] ÷ 10 = 6
70 ÷ 10 = 6
7 ≠ 6 (LHS ≠ RHS)
Option - (3) : (20, 40, 6)
[(20 × 2) + 40] ÷ 10 = 6
[40 + 40] ÷ 10 = 6
80 ÷ 10 = 6
8 ≠ 6 (LHS ≠ RHS)
Option - (4) : (10, 40, 8)
[(10 × 2) + 40] ÷ 10 = 8
[20 + 40] ÷ 10 = 8
60 ÷ 10 = 8
7 ≠ 8 (LHS ≠ RHS)
Hence, "Option - (1)" is the correct answer.