4.2. One sixth of the fourth-grade students received fives on their math test, one third received threes, and half received fours. How many students in this class received unsatisfactory grades?

$$
\text { (4-5 grade) }
$$
4.2. From Figure 12, we see that

$$
\frac{1}{6}+\frac{1}{3}+\frac{1}{2}=\frac{1}{6}+\frac{2}{6}+\frac{3}{6}=1
$$

![](https://cdn.mathpix.com/cropped/2024_05_21_f0d089db3d527e92a992g-26.jpg?height=246&width=508&top_left_y=1856&top_left_x=771)

Fig. 12

i.e., the students who received grades of five, three, and four make up the entire class. Therefore, no student received an unsatisfactory grade.