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A Swedish watch company is assigning ID cards for its employees. The ID is made of 7 digits. How many ID numbers can exist such that at least one of the digits repeat?


Options:
A .   9456745
B .   7898760
C .   8455680
D .   None of these
E .   none of these
Answer: Option C
:
C

Total number of combinations = No repeats + 1 number repeat + 2 number repeat +.....7 number repeat


Total number of combinations - No repeats = 1 number repeat + 2 number repeat +...... 7 number repeat


Total number of combinations - No repeats = Atleast one number repeat


106×9(9.9.8.7.6.5.4)=9000000544320=8455680



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