分类：教育/科学-学习帮助
问题：简单数学题Anarithmeticprogressionhas1 
An arhmetic progression has 12 terms. The sum of all the odd terms is 102 and the sum of all the even terms is 120. Find the first term and the common difference.
回答：解：
a1+a3+a5+……+a11=(a1+a11)+(a3+a9)+(a5+a7)=6a6=102
a6=17
a2+a4+a6+……+a12=(a2+a10)+(a4+a8)+(a6+a12)=4a6+2a9=68+2a9=120
a9=26
d=(26-17)/3=3
a1=17-5×3=2