An Integer from 299 through 1,000, both inclusive, is to be chosen at random. What is the probability that the number chosen will have 2 as at least one of its digit?
Total number of possible numbers between 1000 and 299 = 1000-298 = 702
Lets try to find count of numbers which will have 2.
1. First count of number which will have only one 2
a. Count of numbers with 2 at hundred place =
Fixing 2 at hundred place we have count of = 1
b. Count of numbers with 2 at ten's place =
Fixing 2 at ten's place we have count of = 7*1*9 = 63
c. Count of numbers with 2 at unit's place =
Fixing 2 at unit's place we have count of = 7*9*1 = 63
2. Next lets count numbers which will have exactly 2 two's
7*1*1 = 7
Let the sides of a rectangle be x & y cm, then
Diagonal² = x² + y²
144 = x² + y² ---(i)
Also, Perimeter = 2(x+y) = 28 => (x+y) = 14 ---(ii)
We know, (x+y)² = x² + y² + 2xy
=> 14² = 144 + 2xy
Solving we get
xy = 26