755( 1)1/2-1/4+2/5=(10-5+8)/20=13/20; 2) 3/4-1/2+7/8=(6-4+7)/8=9/8=1ц1/8; 3)1/3-1/9+1/6=(6-2+3)/18=7/18; 4)5/6-2/3+1/4=(10-8+3)/12=5/12;. _______ 756) а)1/2+х=5/6; х=5/6-1/2; х=(5-3)/6; х=2/6; х=1/3. Б)а+1/4=3/4; а=3/4-1/4; а=2/4; а=1/2. В)у-1/5=3/10; у=3/10+1/5; у=(3+2)/10; у=5/10; у=1/2; г)5/6-с=1/3; 5/6-1/3=с; с=(5-2)/6; с=3/6; с=1/2; _______757) 2/3+1/6=(4+1)/6=5/6часа =60:6*5=50минут.