Find the number:

it only has 2 different digits, but they repeat.

the digits appear in the same order in both periods.

the sum of the digits is 20.

the ones digit is 5 more than the tens digit.

the number is?

clue: in math a period is group of 3 digits.

Let's call the digits a and b, a is ones, b is tens

the number will look something like: aba, aba

the sum of all the digits is 20

a + b + a + a + b + a = 20

4a + 2b = 20

2a + b = 20

b is 5 more than a

b = a + 5

2a + (a + 5) = 20 (because b=a+5)

3a + 5 = 20

3a = 15

a = 5

then go back to one of our equations from before to find b:

a + b + a + a + b + a = 20

5 + b + 5 + 5 + b + 5 = 20

b + b = 0

2b = 0

b = 0

therefore the number is 505,505