70. A certain amount was spent on strawberries at 2 r. 40 k. per 1 kg of one variety and the same amount on another variety at 1 r. 60 k. Find the average price of 1 kg of the strawberries purchased.
70. Let the amount spent on each type of strawberry be $a$ r. Then the first type purchased is $a: 2.4=\frac{a}{2.4}$ (kg), and the second type is $-\frac{a}{1.6}$ kg. In total, $\left(\frac{a}{2.4}+\frac{a}{1.6}\right)$ kg were purchased for a total of $2a$ r. The average price per 1 kg is

$$
2 a:\left(\frac{a}{2.4}+\frac{a}{1.6}\right)=\frac{2 \cdot 2.4 \cdot 1.6}{2.4+1.6}=1.92, \text{ i.e., } 1 \text{ r. } 92 \text{ k. }
$$