grammar - "learn to" vs "learn how to" and "teach to" or "teach how to"

Which sounds better:

• learn to or learn how to?


• teach to or teach how to?

I'll make the question clearer with examples.

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a. He taught me to solve sums.
b. He taught me how to solve sums.

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c. I learned to drive a car.
d. I learned how to drive a car.

Answer

He taught me how to solve sums.

I would use this when discussing how a certain individual taught me how to add:

My favorite teacher was Mr. Olson in third grade. He taught me how to solve sums.

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He taught me to solve sums.

I would use this when telling how a certain individual taught me when to add. I probably wouldn't use that sentence as a standalone sentence, but I might say something like:

My dad taught me how to keep my checkbook balanced. He taught me to solve sums on payday, and then to solve subtraction problems for the following two weeks.

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I learned to drive a car.
I learned how to drive a car.

I would interpret these two as pretty much meaning the same thing, because the phrase learning to drive usually means "learning how to drive a car." However, the inclusion or exclusion of how can create a subtle shift in meaning, similar to the one I explained when talking about sums. Consider:

I learned to drive toward the middle of the fairway.
I learned how to drive toward the middle of the fairway.

The second sentence probably means I had a golf instructor teach me how to hit straight shot with my driver off the golf tee:

I used to hook my drives all the times, but then I started taking lessons. After a while, I learned how to drive toward the middle of the fairway.

In contrast, the first sentence might be used in the context of what experience has taught me:

Last summer, I would try to be sneaky on this hole and drive to the left, to get a shorter approach shot. But there are just too many bunkers over there. After about the third or fourth time I took a bogie from the sand, I learned to drive toward the middle of the fairway.