X<500
X=5a+4
X=9b+7
X=11c+9
X=???
Please provide step and formula...
中一數學題
2007-10-04 2:30 am
回答 (7)
2007-10-04 2:41 am
✔ 最佳答案
Observe that (X+2) is divisible by 11 and 9,so (X+2) is divisible by 99.
Also, (X+1) is divisible by 5.
By checking the first few possibilities of X, i.e. (99-2), (198-2), (297-2), (396-2), only (396-2) i.e. 394 is divisibe by 5 after adding 1 to it.
Answer: 394
Hidden assumptions:
1. X>0
2. a,b,c are integers.
2007-10-04 3:20 am
What is a,b,c?
X-4=5a
X-7=9b
X-9=11c
X-4=5a
X-7=9b
X-9=11c
2007-10-04 2:47 am
5a-9b=3
11c-9b=-2
11c+5a=1
.'. -2+9b+5a=1
5a+9b=3
5a-9b=3
10a=6
a=3/5
.'. x=7
11c-9b=-2
11c+5a=1
.'. -2+9b+5a=1
5a+9b=3
5a-9b=3
10a=6
a=3/5
.'. x=7
參考: /
收錄日期: 2021-04-13 13:43:52
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20071003000051KK02550