If eleven plus two equals one, what does nine plus five equal?

Count the number of triangles in the below picture?

A famous swimmer can swim downstream in a lake in exactly 40 minutes with the lake current.
He can swim upstream in that lake in exactly 60 minutes against the lake current.
The length of the lake is 2 km.

How long he can cover the distance of one side at a still lake with no current?

When I go in I might cause pain. I cause you to spit and ask you not to swallow. I can fill your hole. What am I?

People make me, save me, change me, raise me. What am I?

What is the probability of choosing the correct answer at random from the options below?

a) 1/4
b) 1/2
c) 1
d) 1/4

You are mixing a mixture of cement and Sand with five gallons of water. You have a garden hose giving you all the water you need. The problem is that you only have a four-gallon bucket and a seven-gallon bucket and neither has graduation marks. Find a method to measure five gallons.

I have an eye but still cannot see.

Who am I?

In case you were starting to feel confident, this one was meant for third graders in Vietnam. The answer is 66, but we don't blame you for scratching your head about how they got there.

When you say goodbye, I am what you need to tie.
I come as a couple and go wherever you run.
Who am I?