6. Zadatak

$1.$ dan: $18$ kg

$2.$ dan: $18$ kg $+2$ kg $=20$ kg

$3.$ dan: $20$ kg $+2$ kg $=22$ kg (uočimo da vrijedi $18$ kg $+2\cdot2$ kg $=22$ kg)

$\cdots$

$20.$ dan: $18$ kg $+19\cdot2$ kg $=56$ kg

Da bismo izračunali ukupan zbroj, primijenimo Gaussovu dosjetku:

$$\begin{aligned} 18+20+22+\cdots+56&=\\ (18+56)\cdot20:2&=\\ &=740\ \mathrm{kg}. \end{aligned}$$

Lorena je ukupno za tih $20$ dana ubrala $740$ kg jagoda.