Question

There are 45 balloons: 15 are blue; 20 are green; 10 are red. 3 balloons are selected for the float. Leaving your answers in combinatorics format, how many ways can all 3 be selected such that they are the same color.

Answer 1

Answer: Required number of ways =  1715

Step-by-step explanation:

Given, there are 45 balloons: 15 are blue; 20 are green; 10 are red.

3 balloons are selected for the float.

Number of combinations to select r things out of n things : $^nC_r=\dfrac{n!}{r!(n-r)!}$

So, the number of ways to select 3 ballons such that they are the same color = (Ways to select all blue ) x (Ways to select all green ) x (Ways to select all red)

$^{15}C_3+^{20}C_3+^{10}C_3\\\\=\dfrac{15!}{12!\times3!}+\dfrac{20!}{17!\times3!}+\dfrac{10!}{7!\times3!}\\\\=\dfrac{15\times14\times13}{6}+\dfrac{20\times19\times18}{6}+\dfrac{10\times9\times8}{6}\\\\=455+1140+120\\\\=1715$

Hence, Required number of ways =  1715