求助一道Manhattan数学题

想做野猫的但只能做家猫的猫UID: 3686847

How many odd multiples of 7 are there between 100 and 1,000?
这是题目给的解释
The first multiple of 7 that’s greater than 100 is 7 x 15 = 105 (found by trial and error, or by dividing 100 by 7 to first find the multiple of 7 just under 100). Now, to find the largest multiple of 7 under 1,000, we can divide 1,000 by 7, which yields a quotient of 142 and a remainder of 6. However, 7 x 142 = 994 is even. The largest odd multiple of 7 under 1,000 is 994 – 7 = 987. To find the number of terms in the sequence 105, 119, …, 987, we subtract the smallest term from the largest, divide by the step size, and finally add 1 to the result. Note that the step size is 14, not 7, because we are only considering odd multiples of 7:
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The correct answer is 64.
我是这么算的，从100到200有14个7的倍数，200-300,300-400，。900-1000依次也是各14个，其中一半奇数一半偶数，所以7*9=63个，不明白另一个少在哪里

想做野猫的但只能做家猫的猫UID: 3686847

自顶

mpromanusUID: 2565872

300-400之间7的倍数不是14个是15个。

龙猫森林UID: 3723442

300-400之间有15个。我是这么算的：100-1000之间7的奇数倍数从15倍到141倍，15-20之间有3个奇数倍数，20-140之间每10个有5个奇数倍数，5*12=60，还有一个141倍，所以共计：3+60+1=64