Упр.29 Unit 2 ГДЗ Enjoy English 10 класс

29. Read the joke. Explain why was able to is used in it. Can it be replaced with could?
    

    Jones: Aren’t your daughter’s piano lessons costing a fearful lot?
    Brown: On the contrary, I was able to buy the house next door at half its worth.

was able to is used because it means that Brown managed to do something successfully on one particular occasion in the past. He bought the house next door at half its worth.

It cannot be replaced with could here, because could shows general ability in the past, not a single successful action.