Can you replace the question mark with the correct number?

How many triangles are there in the picture below?

You are given with the following sum. Each of the letters can be decoded as a digit. If we tell you that D = 5, then can you solve it entirely?

DONALD
+GERALD
=ROBERT

What can you deduce from the following BrainBat?

CRY
LMKI

When I got four, I have it none.
When I got two, I have it some.
When I got none, I have it all.

What is it?

My friends called me Iron59 because my parents are a chemist and a mathematician. What is my real name?

There's a day, that comes around once a year.
To celebrate the man, you hold dear.
He gave you life, love and will pick you up if you fall.
When it comes to guys like him, He's the best of all.
Who is he?

As you can see that fifteen matches have been used to form an arrangement. What you have to do is remove any six of them to make them ten.

What is in seasons, seconds, centuries and minutes but not in decades, years or days?

Can you think of a smallest +ve number such that if we shuffle the digits of the number, the new number becomes double the original number?