请各位朋友教我解题方法，实在想不通

mataoturku

An instructor scored a student’s test of
50 questions by subtracting 2 times
the number of incorrect answers from
the number of correct answers. If the
student answered all of the questions
and received a score of 38, how many
questions did that student answer
correctly?

13. Which of the following integers does
NOT have a divisor greater than 1 that
is the square of an integer?

In each production lot for a certain toy,
25 percent of the toys are red and 75
percent of the toys are blue. Half the
toys are size A and half are size B. If
10 out of a lot of 100 toys are red and
size A, how many of the toys are blue
and size B?

royalex

An instructor scored a student’s test of
50 questions by subtracting 2 times
the number of incorrect answers from
the number of correct answers. If the
student answered all of the questions
and received a score of 38, how many
questions did that student answer
correctly?

______

设他答对了X道题，那么可以得出如下等式：
38=X-2(50-X),解X=46.

royalex

In each production lot for a certain toy,
25 percent of the toys are red and 75
percent of the toys are blue. Half the
toys are size A and half are size B. If
10 out of a lot of 100 toys are red and
size A, how many of the toys are blue
and size B?

画图

     sizeA   sizeB
Red |______|______|25%
Blue|      |      |75%
     50%      50%
Red&sizeA=10%，=>
 

     sizeA   sizeB

Red |__10%_|__15%_|25%

Blue|  40% |  35% |75%

     50%      50%

所以Blue&sizeB=35%*100=35

mataoturku

Royalex, 你数学也太好了吧，能不能加我，mataoliuxue@msn.com，当我数学老师吧！！