新加坡
今天还是出道英国中学生的数学试题，难度不大，但是需要给出解题步骤。如果在考卷中看到show your working的字样，就是要求你不但要给出答案，还要给出解题过程。类似的prove that字样也是要求给出证明过程的。
见附图的word problem，怎么用英文给出解题步骤呢？参考如下，
(c + 3):(a + 3)= 2:3
(c + 1):(a + 5)= 1:2
then turn the ratios into fractions ⇒
c+3/a+3 = 2/3
c+1/a+5 = 1/2
cross multiply ⇒
3c + 9 = 2a + 6
2c + 2 = a + 5
rearrange ⇒
① 3c - 2a = -3
② 2c -a = 3
solve the simultaneous equations ⇒
② multiply by 2 ⇒ ③ 4c - 2a = 6
③- ① ⇒ c = 9, 9 CHILDREN
Subs. into ①
3•9 - 2a = -3
a = 15, 15 adults
Ratio = 9:15 and in lowest terms, 3:5。真正考试的时候可以简化，保留第一步列联立方程式，rearrange方程式变换求解，还有最后一步化简in lowest terms即可。
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