Ответ:
4 1/2-4/5=9/2-4/5=45/10-8/10= 37/10=3 7/10(кг) или 3,7 кг - вес сухого кирпича
<span>(15+25)*2=80 -периметр</span>
<span>32/8 = 16/4;</span>
<span> 7,5/2,5 = 15/5;</span>
<span>2,5/10 = 1/4;</span>
<span> 2/12 = 3/18;</span>
<span> 9/3 = 24/8;</span>
<span> 4,8/1,2 = 8/2;</span>
<span> 3/12 = 2/8;</span>
<span> 1/42 = 3/126.</span>