Question

Number of permutations of three different things $A,B,C,D$ taking:-

• A. 12
• B. 24
• C. 4
• D. \N

Answer 1

Taking one thing at a time = $A,B,C,D=4$
Taking two things at a time = $AB,AC,AD,BA,BC,BD,CA,CB,CD,DA,DB,DC=12$
Taking three things at a time = $ABC,ACB,ACD,ADC,ABD,ADB,..DAB,DBA,DAC,DCA,DBC,DCB,=24$
Taking five things at a time = we can't take more than four things $=0$