Five friends were comparing how much scrap metal they had brought to the collection. On average, it was $55 \mathrm{~kg}$, but Ivan only brought $43 \mathrm{~kg}$.

How many kg on average did the others bring without Ivan?

(L. Hozová)

Hint. By how many kg does Ivan's contribution differ from the average?
Ivan brought $43 \mathrm{~kg}$, which is $12 \mathrm{~kg}$ less than the (arithmetic) average of all his friends. These $12 \mathrm{~kg}$ correspond to an average of $3 \mathrm{~kg}$ for each of the four remaining friends $(12: 4=3)$.

Without Ivan, the friends brought an average of $58 \mathrm{~kg}$ of iron $(55+3=58)$.

Note. All five friends together brought $275 \mathrm{~kg}$ of iron $(5 \cdot 55=275)$. Without Ivan, the others brought $232 \mathrm{~kg}$ $(275-43=232)$, which is an average of $58 \mathrm{~kg}$ per person $(232: 4=58)$.