MathDB
Counting David's Telephone Numbers

Source:

January 14, 2009

Problem Statement

All of David's telephone numbers have the form 555\minus{}abc\minus{}defg, where a a, b b, c c, d d, e e, f f, and g g are distinct digits and in increasing order, and none is either 0 0 or 1 1. How many different telephone numbers can David have? <spanclass=latexbold>(A)</span> 1<spanclass=latexbold>(B)</span> 2<spanclass=latexbold>(C)</span> 7<spanclass=latexbold>(D)</span> 8<spanclass=latexbold>(E)</span> 9 <span class='latex-bold'>(A)</span>\ 1\qquad <span class='latex-bold'>(B)</span>\ 2\qquad <span class='latex-bold'>(C)</span>\ 7\qquad <span class='latex-bold'>(D)</span>\ 8\qquad <span class='latex-bold'>(E)</span>\ 9