Persons A, B, and C can finish a work in 15, 10, and 12 days respectively. Person B and person C start the work together but are asked to leave after 4 days. In how many days will the remaining work be done by person A?

Rates: $A=\frac{1}{15},\; B=\frac{1}{10},\; C=\frac{1}{12}$ (work/day)

Work done by $B+C$ in 4 days: $4\!\left(\frac{1}{10}+\frac{1}{12}\right)=4\cdot\frac{11}{60}=\frac{11}{15}$

Remaining work: $1-\frac{11}{15}=\frac{4}{15}$

Time for $A$: $\dfrac{\frac{4}{15}}{\frac{1}{15}}=4$ days

Answer: $\boxed{4\text{ days}}$ ✅