Numeracy certainly exists. However, it is very uneven. Some people are only mildly ambidextrous, while others may struggle to determine whether 57 is a higher number than 54 or to add up the change they get back at a store.
It is estimated that about 6% of people have some difficulty with numbers, and number blindness affects both sexes equally.
Dyslexia and numeracy are separate phenomena, but there is a certain connection between them. It is estimated that every seventh person who is dyslexic is also blind to numbers.
Teachers have learned from experience that the numerically blind have the easiest time understanding mathematics presented in a straightforward manner.
A person who is number blind can understand negative numbers more easily if they are presented as degrees of frost on a thermometer.
Numeracy is a relatively new field for researchers.
However, brain scans of numerically blind people are beginning to produce results, and the researchers expect to be able to narrow the circle of the brain centers we use to count and calculate within a short time.