Numbers

age = 12
print(age)

Note that there are no quotes sourrounding the variable value (the number).

Arithmetic

Arithmetic is exactly the same as we write it.

Except multiplication and division are written as * and / respectively.

age = 12

print(age + 1)
print(age - 1)
print(age * 2)
print(age / 2)

These values are different.

Though they both represent numbers to humans, it is not the same for computers.

Computers think all '13' are strings and treat them as such.

So, number methods will not work on '13' nor will string methods work on 13.

Simply, put a '13' in quotes to make it a string.

age = '13'
print(age + '1')

The code above will print 131 because the string is treated as a string.

The code above will print the types of the variables.

age = '13'
print(type(age))

age = 13
print(type(age))

Note that input() returns a string.

a = input("")
b = input("")
print(a + b)

The values are not added, but concated together.

a = input("")
b = input("")
print(int(a) + int(b))