Card sum probability

There are tickets with the numbers 1, 2, 3, 4, 5, 6, 7, and 8 in the envelope. Two tickets are drawn from the envelope at a time. What is the probability that the sum of the numbers drawn will be 7? Write the result as a decimal rounded to hundredths.

Final Answer:

p =  0.11

Step-by-step explanation:

$$\begin{gathered} C_2(8)=\left(\genfrac{}{}{0ex}{}{8}{2}\right)=\frac{8!}{2!(8-2)!}=\frac{8\cdot 7}{2\cdot 1}=28 \\ n=\left(\genfrac{}{}{0ex}{}{8}{2}\right)=28 \\ 7=1+6,2+5,3+4 \\ p=\frac{3}{n}=\frac{3}{28}=0.11 \end{gathered}$$

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