School lunch pupils

A third of the 1st-grade pupils eat lunch and a snack in school, a quarter only have a snack in school and a sixth only have lunch in school. The remainder, 15 pupils, do not go to primary school. How many pupils are there in the 1st grade? And how many are there in each group?

Final Answer:

n =  60
n₁ =  20
n₂ =  15
n₃ =  10

Step-by-step explanation:

$$\begin{gathered} n/3+n/4+n/6+15=n \\ 3n=180 \\ n=\frac{180}{3}=60 \\ n=60 \end{gathered}$$

$n_1=n/3=60/3=20$

$n_2=n/4=60/4=15$

$n_3=n/6=60/6=10$

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