Comparison between ~을 테니까 and ~를 텐데
여러분 안녕하세요~

In the grammar book I have (TOPIK Essential Grammar 150 intermediate) says that 을 테니까 and ~를 텐데 are interchangeable when they mean SUPPOSITION, but that ~을 테니까 cannot be used with interrogative sentences.
They give the following example:
WRONG 길이 막힐 테니까 어떻게 하지요?
RIGHT 길이 막힐 텐데 어떻게 하지요?

However in the student book I have (가나다 korean for foreigners intermediate 1, lesson 5) they say:
(택시 안에서)
헬렌: 이 길말고 다른 길은 없나요?
운전 기사: 이 시간에 서대문 쪽은 한산할 테니까 그리로 갈까요?

Oops~ I am confused, here 테니까 is used with an interrogative sentence!!
When should I use 테니까 or 텐데? ㅠ ㅠ
Any comparison with Spanish would be helpful too :)
Maybe there is an equivalent Korean-Spanish. ^___^
감사합니다! ^^

Question

Comparison between ~을 테니까  and ~를 텐데
여러분 안녕하세요~

In the grammar book I have (TOPIK Essential Grammar 150 intermediate) says that 을 테니까 and ~를 텐데 are interchangeable when they mean SUPPOSITION, but that ~을 테니까 cannot be used with interrogative sentences.
They give the following example: 
WRONG> 길이 막힐 테니까 어떻게 하지요?
RIGHT> 길이 막힐 텐데 어떻게 하지요?

However in the student book I have (가나다 korean for foreigners intermediate 1, lesson 5)  they say:
(택시 안에서)
헬렌: 이 길말고 다른 길은 없나요?
운전 기사: 이 시간에 서대문 쪽은 한산할 테니까 그리로 갈까요?

Oops~ I am confused, here 테니까 is used with an interrogative sentence!!
When should I use 테니까 or 텐데? ㅠ ㅠ
Any comparison with Spanish would be helpful too :) 
Maybe there is an equivalent Korean-Spanish. ^___^ 
감사합니다! ^^

Answer

~할 텐데 is used when we don't know about a situation perfectly. 
→ 길이 막힐 텐데 어떻게 하지요? : he or she have not reached the way so he or she should use 막힐 텐데 
~할 테니까 is used when we know about a situation with conviction.
→ 이 시간에 서대문 쪽은 한산할 테니까 그리로 갈까요? : This taxi driver knows well about roads. Therefore, he should use 테니까

Answer

I don't think there's any English or Spanish equivalent of -ㄹ 테니까 in this case. 
I can only think of a couple of examples. 

Tú quédate ahí calladito, porque voy a ir allá. 
내가 거기 갈 테니까 거기 꼼짝말고 서 있어요. 

Será difícil aprender a hablar Alemán, así... Quieres mi ayuda? 
독일어 배우기 힘들 테니까 도와줄까?

Answer

Thank you!

Answer

~할 텐데 is used when we don't know about a situation perfectly.
→ 길이 막힐 텐데 어떻게 하지요? : he or she have not reached the way so he or she should use 막힐 텐데

~할 테니까 is used when we know about a situation with conviction.
→ 이 시간에 서대문 쪽은 한산할 테니까 그리로 갈까요? : This taxi driver knows well about roads. Therefore, he should use 테니까