求 数学JJ--26题

27.           less than or equal to n 的数的sum=n(n+1)/2,T为multiple 5 and less than or equal to 50的数的sum, S为multiple 6 and less than or equal to 60的数的sum,问T-S?

我选60,我没用上题目给的公式,是把数字一个个列出来算的,幸好不多,但不知有没理解错MingLiU","serif"; mso-bidi-font-family: PMingLiU; mso-fareast-language: ZH-TW; mso-ansi-language: EN-US; mso-bidi-language: AR-SA;">

我算出来是55的啊 ??

MingLiU","serif"; mso-bidi-font-family: PMingLiU; mso-fareast-language: ZH-TW; mso-ansi-language: EN-US; mso-bidi-language: AR-SA;">我的解法:    一共10个数字, 5和6相差1  10和12相差2 .....是个等差么,也就是(1+10)*10/2这样不是55吗 ??