Problem:
7×539=
Answer Choices:
A. .7×53.9
B. .7×.53.9
C. .7×5.3.9
D. 7×.53.9
E. .07×.53.09
Solution:
To get .9 in the numerator, we must divide it by 10. To maintain equality, we must also divide the denominator by 10. Thus
107×53109=107×53109=.7×53.9.
In all other cases, the resulting fraction is 101 or 1001 of the original fraction.
Answer: A.
The problems on this page are the property of the MAA's American Mathematics Competitions