Explanation:

- Raju completes the whole work in 20 days.

- This means Raju finishes 1/20 of the work each day.

- Raju worked for 5 days, so he completed 5/20 (or 1/4) of the work.

- This leaves 3/4 of the work remaining.

- Jakob finished the remaining 3/4 of the work in 15 days.

- Thus, Jakob completes 3/4 * 1/15 = 1/20 of the work each day.

- Both Raju and Jakob together complete 1/20 + 1/20 = 1/10 of the work each day.

- Therefore, they can finish the entire work together in 10 days.

- Option:1, 20 days - Too long

- Option:2, 12 days - Slightly off

- Option:3, 10 days - Correct

- Option:4, 16 days - Not plausible

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