Work done by A and B in one day = 1/12. Work done by B and C in one day = 1/15. Let work done by B in one day = x. Then, A's work = 1/12 - x and C's work = 1/15 - x. Solving gives A + B + C = 1/8. Therefore, they will complete the work in 8 days.

Work done by A in one day = 1/10. Work done by B in one day = 1/15. Together, they do (1/10 + 1/15) = 1/6. Therefore, they will complete the work in 6 days.

Simple Interest = Principal * Rate * Time / 100 = 2000 * 5 * 3 / 100 = $300.

A's income = B's income + 20% of B's income = 5000 + 0.2 * 5000 = 5000 + 1000 = $6000.

If 5 workers take 10 days, then 10 workers will take 10/2 = 5 days.

If A is twice as good as B, then B will take twice the time of A. A takes 20 days, so B will take 20 * 2 = 40 days.