DS question?

[rahi08]

can anybody explain this?

[Morgoth]

can anybody explain this?

1st gadget = C
2nd gadget = C/2 = C/2^1
3rd gadget = C/4 = C/2^2
4th gadget = C/8 = C/2^3
5th gadget = C/16 = C/2^4
-
-
-
9th gadget = C/2^8

so on and so forth

(1) the sum of the costs of the third and forth gadget -$9
C/2^2 + C/2^3 = 9
You can easily solve for C. Sufficient.

(2) the sum of the costs of the second and ninth gadget is $24(2^7+1)/28
C/2 + C/2^8 = 24(2^7+1)/28
You can easily solve for C. Sufficient.

Thus, D is the answer.

[rahi08]

Thanks for your explanation.