By the age of ____ years, most children have learned the addition ...

[saraeharris]

By the age of ____ years, most children have learned the addition tables so well that the sums of single digit numbers can be retrieved from memory rather than recalculated.
 
  a. eight or nine
  b. six or seven
  c. five or six
 d. three or four

Question 2

American teenagers may be less healthy than their parents at the same age because of
 
  a. an increase in the incidence of infectious diseases.
  b. an increase in the incidence of physical illnesses.
  c. lifestyle and risky behavior.
  d. a surge in cases of adolescent cancer.

[ladyjames123]

Answer to Question 1

a

Answer to Question 2

c