Question

What is the largest number of positive integer to be picked up randomly so that the sum or difference of any two of the chosen number is divisible by 10?
1. 2
2. 5
3. 7
4. 10

Answer 1

Correct Answer - Option 3 : 7

Calculation:

Let number be 10k, 10k + 1, 10k + 2,..... 10k+ 9

Sum of number is divisible by 10:

Possible combination are: (10k, 10k), (10k + 1, 10k + 9), (10k + 2, 10k + 8), (10k + 3, 10k + 7), (10k + 5, 10k + 5) and (10k + 4, 10k + 6) 

Difference of number is divisible by 10:

Possible combination are: (10k, 10k) 

Total combination of the  sum or difference of any two of the chosen number is divisible by 10 is 7