Factoring Factorials (Source: Mathcounts)

Algebra Level 1

What is 7 ! + 6 ! 8 \dfrac {7!+6!}8 ?

840 630 720 660

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3 solutions

Trí Onii-sama
Nov 22, 2014

7 ! = 6 ! × 7 = > 7 ! + 6 ! = 6 ! ( 1 + 7 ) = 6 ! × 8 = > ( 7 ! + 6 ! ) 8 = 6 ! × 8 8 = 6 ! = 720 7!=6! \times 7=>7!+6!=6!(1+7)=6! \times 8=>\frac{(7!+6!)}{8}=\frac {6! \times 8}{8}=6!=720

7 ! + 6 ! 8 = 6 ! ( 7 + 1 ) 8 = 6 ! × 8 8 = 6 ! = 720 \color{midnightblue}{\frac{7!+6!}{8}=\frac{6!(7+1)}{8}=\frac{6!\times8}{8}=6!=\boxed{720}}

Lew Sterling Jr
May 28, 2019

7 ! + 6 ! 8 = ( 1 2 3 4 5 6 7 ) + ( 1 2 3 4 5 6 ) 8 = 5760 8 = 720 \frac{7!+6!}{8}=\frac{(1\cdot 2\cdot 3\cdot 4\cdot 5\cdot 6\cdot 7)+(1\cdot 2\cdot 3\cdot 4\cdot 5\cdot 6)}{8}=\frac{5760}{8}=\mathbf{720}

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