Foizlar

Foiz — sonning yuzdan bir ulushi: $1\,\% = \dfrac{1}{100} = 0{,}01$. Foizli masalalar uch turga bo'linadi.

Uch asosiy masala

1. Sonning foizini topish: $a$ ning $p\,\%$ i $= a \cdot \dfrac{p}{100}$. $240$ ning $15\,\%$ i: $240 \cdot 0{,}15 = 36$.
2. Foiziga ko'ra sonning o'zini topish: $x$ ning $p\,\%$ i $b$ ga teng bo'lsa, $x = b : \dfrac{p}{100}$. $36$ — qaysi sonning $15\,\%$ i? $36 : 0{,}15 = 240$.
3. Qism necha foiz: $\dfrac{b}{a} \cdot 100\,\%$. $36$ soni $240$ ning $\dfrac{36}{240} \cdot 100 = 15\,\%$ i.