Link 1: http://i42.tinypic.com/zu2fwj.png
Link 2: http://i40.tinypic.com/e8rhvs.png
Please help me. I do not know how to solve for n. Thank you.
Link 1: http://i42.tinypic.com/zu2fwj.png
Link 2: http://i40.tinypic.com/e8rhvs.png
Please help me. I do not know how to solve for n. Thank you.
Link1: $\displaystyle ^nP_8 = 13 \cdot ^nP_7$.
Substitute the definition $\displaystyle ^nP_r$ and simplify. Then solve the resulting simple linear equation for n. Note that (n - 7)! = (n - 7)(n - 8)!
Link2: $\displaystyle ^nP_6 = 90 \cdot ^nP_4$.
Done in a similar way. Yiou will end up with a quadratic equation to solve. Note that one of the solutions to this quadratic equation is not be valid.