To express a number as a percentage, you need to write it as a ratio with denominator 100.
We know that ratios have different forms they can be written into, for example, all the following are equivalent:
[tex] \cfrac{3}{7} = \cfrac{30}{70} = \cfrac{9}{21} = \cfrac{15}{35} = \ldots [/tex]
So, since 43 students out of 860 are sick, the ratio of sick students is
[tex] \cfrac{43}{860} [/tex]
and we want to express this as a ratio with denominator 100, so we have
[tex] \cfrac{43}{860} = \cfrac{x}{100} [/tex]
So, if we solve for x, we have
[tex] x = \cfrac{43\cdot 100}{860} = \cfrac{4300}{860} = 5 [/tex]
So, 5% of students is sick.
