Question
Two circles are externally tangent to each other. The
first circle, centered at X, has a radius of 8 cm, while the second circle, centered at Y, has a radius of 5 cm. Determine the length of their common tangent MN.Solution
ATQ;

6 6 13 39 ? 226
...56. 23Â Â Â Â Â 45Â Â Â Â Â 89Â Â Â Â Â 177Â Â Â Â Â 363Â Â Â Â Â 705
...12, 6, 6, 9, 18, ?
1,2, 5, ‘?’, 41, 122, 365
4                14                  130                     512                �...
Select the number from among the given options that can replace the question mark (?) in the following series.
2, 6, 12, 20, ?, ?
32Â Â Â 96Â Â Â Â 240Â Â Â Â 480Â Â Â Â Â 720Â Â Â ?
3601 3602 1803 604 154 36
...76, 82, 158, 240, 398, 638, ?
7    7       14    42   ?     840
...