If 21x = 79x, what is the value of x?

How many triangles are there in the picture below?

I am an odd number. Take away a letter and I become even. What number am I?

How do you go from 98 to 720 using just one letter?

Can you find out the smallest number that can be conveyed as the sum of three squares in three unique ways?

Look at this sequence from top to bottom. What is the next number in the sequence?
1
11
21
1211
111221
312211

Double it and multiply it by 4. Then divide it by 8 and you’ll have it once more. What number is it?

A girl is twice as old as her brother and half as old as her father. In 50 years, her brother will be half as old as his father. How old is the daughter now?

How many triangles are there on the puzzle below?

What is next number in the pattern below:

131 517 192 123 ?