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There are 31 students in a class. The mathematics score wasn't worse than 2. The average score in mathematics was 2.

How many students have a score of one, and how many have a score of 2?

Correct answer:

n(1) =  0
n(2) =  31

Step-by-step explanation:

$$\begin{gathered} (1\cdot a+2\cdot b)/31=2 \\ a+b=31 \\ a+2b=62 \\ a+b=31 \\ a=n(1)=0 \end{gathered}$$

$b=n(2)=31$

(1·a+2·b)/31 = 2
a+b=31

a+2b = 62
a+b = 31

Row 2 - Row 1 → Row 2
a+2b = 62
-b = -31


b = -31/-1 = 31
a = 62-2b = 62-2 · 31 = 0

a = 0
b = 31

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