Calculated 67234

There are 13 boys and 17 girls in the class. The weeklies are always either two girls or a boy and a girl. The teacher calculated that she has 357 ways to create a pair of weekly newspapers. However, Anetka did not come to school on Monday morning. How many options does the teacher have to choose a pair of weekly newspapers?

Correct answer:

n₂ =  328

Step-by-step explanation:

$$\begin{gathered} a=13 \\ b=17 \\ {n}_1=a\cdot b+b\cdot (b-1)/2=13\cdot 17+17\cdot (17-1)/2=357 \\ c=b-1=17-1=16 \\ {n}_2=a\cdot c+c\cdot (c-1)/2=13\cdot 16+16\cdot (16-1)/2=328 \end{gathered}$$

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