1. Tính nhanh a, 0,5 + 1/3 +0,4 + 5,7 + 1,6 – 4/35 b, 8,9 – 1/27 – 1/56 -1\42 -1/30 – 1/20 – 1/12 – 1/6 – 1/2 2. 3/35 – ( 3/5 + x ) = 2/7

0 bình luận về “1. Tính nhanh a, 0,5 + 1/3 +0,4 + 5,7 + 1,6 – 4/35 b, 8,9 – 1/27 – 1/56 -1\42 -1/30 – 1/20 – 1/12 – 1/6 – 1/2 2. 3/35 – ( 3/5 + x ) = 2/7”

1. a) `0,5 + 1/3 + 0,4 + 5,7 + 1,6 – 4/35`

   `=1/2 + 1/3 + 2/5 + 57/10 + 8/5 – 4/35`

   `=( 1/2 + 2/5 + 57/10) + (1/3 + 8/5) – 4/35`

   `=33/5 + 29/15 – 4/35`

   `=128/15 – 4/35`

   `=884/105` 

   b) `8,9 – 1/27 -1/56 – 1/42 – 1/30 – 1/20 – 1/12 – 1/6- 1/2`

   `= 8,9 -( 1/2 + 1/6 + 1/12 +1/20 + 1/30 + 1/42 + 1/56 + 1/27)`

   `= 8,9- ( 1/1.2 + 1/2.3 + 1/3.4 + 1/4.5 + 1/5.6 + 1/6.7 + 1/7.8 + 1/27)`

   `= 8,9 – ( 1/1 -1/2+ 1/2-1/3+…+1/7-1/8 + 1/27)`

   `=8,9 – ( 1- 1/8 + 1/27)`

   `= 89/10- 197/216`

   `=8627/1080`

   2. 

   `3/35 – ( 3/5 +x) = 2/7`

   `=> 3/5+ x = 3/35 – 2/7`

   `=> 3/5 + x= -1/5`

   `=> x= -1/5 – 3/5`

   `=> x= -4/5`

   Vậy `x= -4/5`

    

   Bình luận

2. Giải thích các bước giải:

   Bài `1`
   `a)`
   `0,5 + 1/3 +0,4 + 5,7 + 1,6  – 4/35`
   `=1/2+1/3+2/5+57/10+8/5-4/35`
   `=(1/2+1/3)+(2/5+8/5+57/10)-4/35`
   `=(3/6+2/6)+(4/10+16/10+57/10)-4/35`
   `=5/6+77/10-4/35`
   `=50/60+462/60-4/35`
   `=512/60-4/35`
   `=884/105`
   `b)`
   `8,9-1/27-1/56-1/42-1/30-1/20-1/12-1/6-1/2`
   `=89/10-1/27-1/56-1/42-1/30-1/20-1/12-1/6-1/2`
   `=89/10-(1/27+1/56+1/42+1/30+1/20+1/12+1/6+1/2)`
   `=89/10-(1/27+1/7.8+1/6.7+1/5.6+1/4.5+1/3.4+1/2.3+1/1.2)`
   `=89/10-1/27-(1/1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8)`
   `=89/10-1/27-(1/1-1/8)`
   `=89/10-1/27-7/8`
   `=2403/270-10/270-7/8`
   `=2393/270-7/8`
   `=19144/2160-1890/2160`
   `=17254/2160`
   Bài `2`
   `3/35-(3/5+x)=2/7`
   `=>3/35-3/5-x=2/7`
   `=>3/35-21/35-x=2/7`
   `=>-18/35-x=2/7`
   `=>x=-18/35-2/7`
   `=>x=-18/35-10/35`
   `=>x=-4/5`
   Vậy `x=-4/5`

   Bình luận