№ 1821

а) 7 3/17+8 5/17-1 6/17=

=15 8/17-1 6/17=

=14 2/17

б) 5 7/10-(4 3/10-2 1/10)=

=5 7/10-2 2/10=

=3 5/10=3 1/2

А где 1838?

1) 7 3/17 + 8 5/17 - 1 6/17 = (7 + 8 - 6) + (3/17 + 5/17 - 6/17) = 9 2/17 

2) 5 7/10 - (4 3/10 - 2 1/10) = 5 7/10 - 2 2/10 = (5 - 2) + (7/10 - 2/10) = 3 5/10

3)10 7/15 - 3 1/15 + 4 4/15 = (10 - 3 + 4) + (7/15 - 1/15 + 4/15) = 11 10/15

4) 9 9/11 - (3 2/11 - 2 3/11) = 9 9/11 - 10/11 = 8 10/11