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Question
In the following number, replace * by the smallest number to make it divisible by 11:
39*43
Solution
39*43
Sum of the digits at odd places = 3 + * + 3 = 6 + *
Sum of the digits at even places = 4 + 9 = 13
Difference = sum of odd terms – sum of even terms
= 6 + * – 13
= * – 7
Now, (* – 7) will be divisible by 11 if * = 7.
i.e., 7 – 7 = 0
0 is divisible by 11.
∴ * = 7
Hence, the number is 39743.
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Using divisibility tests, determine which of the following numbers are divisible by 2; by 3; by 4; by 5; by 6; by 8; by 9; by 10; by 11 (say, yes or no):
|
Number |
Divisible by |
||||||||
|
2 |
3 |
4 |
5 |
6 |
8 |
9 |
10 |
11 |
|
|
128 |
Yes |
No |
Yes |
No |
No |
Yes |
No |
No |
No |
|
990 |
______ | ______ | ______ | ______ | ______ | ______ | ______ | ______ | ______ |
|
1586 |
______ | ______ | ______ | ______ | ______ | ______ | ______ | ______ | ______ |
|
275 |
______ | ______ | ______ | ______ | ______ | ______ | ______ | ______ | ______ |
|
6686 |
______ | ______ | ______ | ______ | ______ | ______ | ______ | ______ | ______ |
|
639210 |
______ | ______ | ______ | ______ | ______ | ______ | ______ | ______ | ______ |
|
429714 |
______ | ______ | ______ | ______ | ______ | ______ | ______ | ______ | ______ |
|
2856 |
______ | ______ | ______ | ______ | ______ | ______ | ______ | ______ | ______ |
|
3060 |
______ | ______ | ______ | ______ | ______ | ______ | ______ | ______ | ______ |
|
406839 |
______ | ______ | ______ | ______ | ______ | ______ | ______ | ______ | ______ |
