90+70=160 км/ч скорость сближения
1600:160=10 часов
Ответ: через 10 часов они встретятся
5/6 + 1/8 = (5 × 4 + 1 × 3)/24 = 20/24 + 3/24 = 23/24
13/15 - 1/3= (13 × 1 - 1 × 5)/15 = 13/15 - 5/15 = 8/15
8/21 - 2/7 = <span>(8 × 1 - 2 × 3)/21 = 8/21 - 6/21 = 2/21
</span>1/2 + 1/3 =<span>(1 × 3 + 1 × 2)/6 = 3/6 + 2/6 = 5/6
</span>2/7 - 1/9 =<span>(2 × 9 - 1 × 7)/63 = 18/63 - 7/63 = 11/63</span>
502 1 -4x-4y+28 2 -14+2a+2b 3 3c-24-13d 4 -1a-2+3c 5 -6a+8b+9 6 -15c+10b+12 503 1 2(-2y+3) 2 3(3c-a-2b) 3 5(m-25+5n) 4 x(-4-3-9) 5 a(1.3-2-6.5) 6 b(2.1+3.5-4.7)