While brazilian and columbian street children who earn their money as vendors were able to conduct financial operations in their minds, when asked to perform similar tasks with a paper and pencil they

When asked to perform similar tasks with a paper and pencil they "performed worse than without using paper and pencil ".

It is conceivable to be better at mental count and the reason can be that those children’s daily lives are based on these calculations in their heads, practice helps, but when it comes to writing down the mathematics there are many hurdles for such kids like unfamiliarity with the concept of solving on paper and in some cases dyslexia etc.

answer:

d. because dr. laguardia selected a widely used measure, his study generalizes to has strong external validity. external validity has limited external validity. other applications of this measure.

the widely used measure that he applied to his experiment was the benton facial recognition test. it employed on to football players and as result, only players who suffered brain concussions did not pas this test. and although it has an external validity, it is limited because it isn't general to apply to other population.

well, there are a lot of places we get information about earth from. like science classes, websites, books, newspapers, etc.