Question

Would time taken to train n-random forest be equal to n x decision trees

Answer 1

No, the time to train the random forest and n - decision tree won't be same because random forest picks a subset of data or features or even both for each of the sub-tree, sometimes it might create some shallow (smaller) trees as well. Hence time to train the random forest and decision tree won't be the same. Further reading on the random forest: https://bit.ly/2u7erIB