Certificate

There is 31 students in a class. From mathematics was'nt worse mark than 2. Average mark in mathematics was 2.

How many students have mark 1 and how many mark 2?

Correct result:

n(1) =  0
n(2) =  31

Solution:

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

$b=n(2)=31$

(1•a+2•b)/31 = 2
a+b=31

a+2b = 62
a+b = 31

a = 0
b = 31

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