Question

Tính bằng cách hợp lý

a)\(\dfrac{7}{15}\)-(\(\dfrac{2}{15}\)-\(\dfrac{12}{18}\))

b) (\(\dfrac{7}{41}\)-\(\dfrac{4}{9}\))-(\(\dfrac{3}{19}\)+\(\dfrac{7}{41}\))+(\(\dfrac{4}{9}\)-\(\dfrac{16}{19}\))

Answer 1

a) 7/15-(2/15-12/18)

=7/15-2/15+2/3

=5/15+2/3

=1/3+2/3

=1

b)(7/41- 4/9) - (3/19 + 7/41) + (4/9 - 16/19)

=7/41 - 4/9 - 3/19 - 7/41 + 4/9 + 16/19

=(7/41 - 7/41) - (4/9 - 4/9) - (3/19 + 16/19)

= -1

Answer 2

b) 7/41 - 4/9 - 3/19 - 7/41 + 4/9 + 16/19

= (7/41 - 7/41 ) - (4/9 - 4/9 ) + ( 3/19 + 16/19 )

= 0 - 0 + 1

= 1