In the following number series, a number is missing. Find out that missing number. 10 ? 340 780 1660 3420

Pattern analysis: 10 to 340 (×3.4), 340 to 780 (×2.29), 780 to 1660 (×2.13), 1660 to 3420 (×2.06). More systematic: differences are 330, 440, 880, 1760. Each difference (after the first) is double the previous. So next difference should be 1760×2 = 3520. 3420 + 3520 = 6940 (not an option). Alternative: 10, 120, 340, 780, 1660, 3420. Working backwards: if missing is X, then X to 340 fits the doubling pattern. If 120 is the missing term: 120→340 (+220), 340→780 (+440, double of 220), 780→1660 (+880, double of 440), 1660→3420 (+1760, double of 880). The pattern holds perfectly with 120. Answer is 120 (Option C).