3 /4*2/9=1/6
12/13*13/15=12/15=0,8
<span>в) 8/21*7/10=4/15</span>
<span><span>г) 7/5*15/14=3/2=1,5</span></span>
<span><span><span>д) 8/15*25/28=10/21</span></span></span>
<span><span><span><span>е) 2/15 * 5 /22=1/33</span></span></span></span>
<span><span><span><span><span>ж)9*5/6=15/2=7,5</span></span></span></span></span>
<span><span><span><span><span><span>з) 1/2*4=2</span></span></span></span></span></span>
<span><span><span><span><span><span><span>и) 4*5/9=20</span></span></span></span></span></span></span>
=(1/5)^20· 5^21 + (2·5)^6 :10^5=5^ (-20)· 5^21 +10^6:10^5= 5+10=15.
50+80=130 км/ч - скорость удаления
130*3=390 км - расстояние между ними через 3 часа
1) 1 4/20-3/20= 1 1/20 м - ширина
2) (1 4/20+1 1/20)*2= 4 1/2 или 4,5 м - периметр