In the number series 5, 10, 20, 40, the next term is _______. – UGC NET Question

Each term is obtained by multiplying the previous term by 2: 5×2 = 10, 10×2 = 20 and 20×2 = 40. This defines a geometric progression with ratio 2. Applying the same rule gives 40×2 = 80. Thus, 80 is the correct next term that preserves the doubling pattern.

Option A:
Option A is 60, which would represent adding 20 to 40 rather than doubling. No earlier transition uses simple addition of a fixed number, so 60 does not fit the rule.

Option B:
Option B is 70, which involves adding 30 to 40 and lacks any basis in the preceding behaviour of the sequence. It fails to keep the constant ratio property. Hence, it is incorrect.

Option C:
Option C equals 80 and results directly from 40×2. The extended series 5, 10, 20, 40, 80 shows a clean geometric pattern. This makes 80 the unique choice that follows the same logic.

Option D:
Option D is 100, which would require a factor of 2.5 from 40. As the sequence has consistently used a ratio of 2, introducing 2.5 is unjustified. Therefore, this option is not valid.