267题JJ答案是不是错了

weiweichenyang · 发表于 2011-3-15 10:28:12

267.If n is an integer between 10 and 99 and n is divisible by 7, the remainder is 3, is n< 80?
1) When n is divided by 5, the remainder is 0
2) When n is divisible by 3, the reminder is 0
Inclusive ?

n = 7m + 3

from 1) à n = 5k à n = 35t + 10, t = 0, 1, 2, 3, … sonot A

from 2) à n = 3s à n = 21a + 24a = 0, 1, 2, 3, …sonot B

union à n = 35t + 10 , n = 3s à n = 105 k + 45 在 10 到 99 只有45满足条件 so C

好像上面的答案忽略了n is an integer between 10 and 99

hehehe21 · 发表于 2011-3-15 10:43:04

就是因为只在10-99才唯有45满足，结合1，2可确定。100以上还有其他的

weiweichenyang · 发表于 2011-3-15 10:56:55

当 n is an integer between 10 and 99 时满足n is divisible by 7, the remainder is 3和When n is divisible by 3, the reminder is 0 条件的有
10 45 66 87，知道了，谢谢你

267题JJ答案是不是错了

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