Question

[Dương ♡]

   Tính nhanh:

a, 891 + ( 359 + 109 )                             b, 19/11 + ( 5/13 + 3/11 )

           c, 1/5 + 4/10 +9/15 + 16/20 + 25/25 + 36/30 + 49/35 + 64/40 + 81/45

Answer 1

[I am➻Minh]

\(a,=\left(891+109\right)+359\)

\(=1000+359\)

\(=1359\)

\(b=\left(\frac{19}{11}+\frac{3}{11}\right)+\frac{5}{13}\)

\(=2+\frac{5}{13}=\frac{31}{13}\)

\(c,=\frac{1}{5}\left(1+2+3+4+5+6+7+8+9\right)\)

\(=\frac{1}{5}\cdot45=9\)

Answer 2

[Bùi Thị Nguyệt Ánh]

a)=891+359+109

=(891+109)+35

=1000+359=1359

b)=19/11+5/13+3/11

=(19/11+3/11)+5/13

=2+5/13=31/13

c)=1/5+2/5+3/5+4/5+5/5+6/5+7/5+8/5+9/5

=(1/5+9/5)+(2/5+8/5)+(3/5+7/5)+(4/5+6/5)+5/5

=1+1+1+1+1=5