Maths · The fundamental principle of counting
The number of two-digit numbers which are of the form with are given by
The number of two-digit numbers which are of the form \( x y \) with \( y<x \) are given by
- A. 60
- B. 55
- C. 50
- D. 45
Step-by-step solution
For two-digit numbers of the form xy where y < x, x can be from 1 to 9, and y can be from 0 to x-1. For each x, there are x choices for y. Summing from x=1 to 9 gives 1+2+...+9 = 45.
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