ok so here we go....

the problem states the following...

S(L)= 3L -20.5

the function s defined above can be used to approximate a womans shoe size in the united states, where L is the womans foot length in inches. according to this function, which of the following best approximates the shoe size of a woman whose foot length is 9.3 inches.

a. 5.5

b. 6

c. 6.5

d. 7

e. 7.5

ok well 9.3 inches is approx .779 ft or something like that. when i plugged 7 in the problem i got .5 ft and when i plugged in 7.5 i got 2 ft. so i chose d, and said that 7 is closest to the womans foot. of course the book says im wrong, im just not understanding why, the error with 7 is smaller then with 7.5...

thanks in advance.

note this problem came from the may 2011 sat test section 4 problem 7.