How many distinct four-digit numbers can be formed by the digits {1, 2, 3, 4, 5, 5, 6, 6}? Options.
A) 280	B) 360	C) 486	D) 560	E) 606
Option 1: each group of 4 different digits will produce 4!=24 four-digit numbers   - Option 2: each group of 4 digits that contains two 5's will produce 4!/2=12 four-digit numbers   - Option 3: same with option 2 -&gt; 4!/2=12 four-digit numbers   - Option 4: 4!/4=6 four-digit numbers   In total, there are: 15*24 + 10*12 + 10*12 + 1*6= 
<gadget id="calculator">15*24 + 10*12 + 10*12 + 1*6</gadget>
<output>606</output>
606 four-digit numbers.   ANSW606R:606
<result>E</result>
How many distinct four-digit numbers can be formed by the digits {1, 2, 3, 4, 5, 5, 6, 6}?