>Recently one of my students asked me to help with statistics. So, we work with Kaplan AP Statistics. There I see:
>"...decrease the margin of error by a factor of 1/4...."
>
>Just curious, is this passage completely understandable for those of you how was born in English language environment?

Nope. Dragan has it right. Read as written, it means to multiply the margin of error by a factor of 4.

Tamar