4177

13400

3400

5200

4000

4177

13400

3400

5200

4000

29 . 87 - 29 . 23 + 64. 71 = 6400

125 x 72 x 5 = 125 x 8 x 9 x 5 = 1000 x 45 = 45000

3 x 4 x 19 + 6 x 71 x 2 + 120

= 12 x 19 + 12 x 71 + 12 x 10

= 12 x ( 19 + 71+10)

= 12 x 100

= 1200

125 x 72 x 5 = 125 x 8 x 9 x 5 = 1000 x 45 = 45000

3 x 4 x 19 + 6 x 71 x 2 + 120

= 12 x 19 + 12 x 71 + 12 x 10

= 12 x ( 19 + 71+10)

= 12 x 100

= 1200

125 x 72 x 5 = 9000 . 5 = 45000

3 x 4 x 19 + 6 x 71 x 2 + 120

= 12 x 19 + 12 x 71 + 12 x 10

= 12 x (19 + 71 + 10)

= 12 x 100

= 1200

92 + 71 + 108 = (92 + 108) + 71 = 200 + 71 = 271

32 x 47 + 53 x 47 + 47 x 15 = 47(32 + 53 + 15)

                                         = 47.100

                                         = 4700

90 x 143 - 43 x 90 = 90.(143 - 43) = 90.100 = 9000

(1200 + 60) : 12 = 1800 : 12 = 150

2 x 18 x 24 + 3 x 50 x 16 + 12 x 32 x 4 = 18.(2.24) + 50.(3.16) + 32.(12.4) = 18.48 + 50.48 + 32.48 = 48(18 + 50 + 32) = 48.100 = 4800

92+71+108=71+92+108=71+200=271

92+71+108=71+(92+108)=71+200=271

90x143-43x90=90x(143-43)=90x100=9000

32x47+53x47+47x15=47x(32+53+15)=47x100=4700

(1200+60):12=1260:12=105

2x18x24+3x50x16+12x32x4=(2x24)x18+(3x16)x50+(12x4)x32

=48x18+48x50+48x32

=48x(18+50+32)

=48x100=4800

\(\frac{5}{6}+\frac{11}{12}+\frac{19}{20}+...+\frac{89}{90}\)

\(=1-\frac{1}{6}+1-\frac{1}{12}+1-\frac{1}{20}+...+1-\frac{1}{90}\)

\(=8-\left(\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{90}\right)\)

\(=8-\left(\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{9.10}\right)\)

\(=8-\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+....+\frac{1}{9}-\frac{1}{10}\right)\)

\(=8-\left(\frac{1}{2}-\frac{1}{10}\right)\)

\(=\frac{38}{5}\)

100/11

hok tốt

`Answer:`

a) \(\frac{5}{6}+\frac{11}{12}+\frac{19}{20}+\frac{29}{30}+\frac{41}{42}+\frac{55}{56}+\frac{71}{72}+\frac{89}{90}\)

\(=1-\frac{1}{6}+1-\frac{1}{12}+1-\frac{1}{20}+1-\frac{1}{30}+1-\frac{1}{42}+1-\frac{1}{56}+1-\frac{1}{72}+1-\frac{1}{90}\)

\(=8-\frac{1}{6}-\frac{1}{12}-\frac{1}{20}-\frac{1}{30}-\frac{1}{42}-\frac{1}{56}-\frac{1}{72}-\frac{1}{90}\)

\(=8-\left(\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}+\frac{1}{90}\right)\)

\(=8-\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}+\frac{1}{9}-\frac{1}{10}\right)\)

\(=8-\frac{2}{5}\)

\(=\frac{38}{5}\)

b) \(\frac{1}{2}+\frac{5}{6}+\frac{11}{12}+\frac{19}{20}+\frac{29}{30}+\frac{41}{42}+\frac{55}{56}+\frac{71}{72}+\frac{89}{90}\)

\(=1-\frac{1}{2}+1-\frac{1}{6}+1-\frac{1}{12}+1-\frac{1}{20}+1-\frac{1}{30}+1-\frac{1}{42}+1-\frac{1}{56}+1-\frac{1}{72}+1-\frac{1}{90}\)

\(=9-\left(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}+\frac{1}{90}\right)\)

\(=9-\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}+\frac{1}{9}-\frac{1}{10}\right)\)

\(=9-\left(1-\frac{1}{10}\right)\)

\(=\frac{81}{10}\)

\(=\left(1-\dfrac{1}{2}\right)+\left(1-\dfrac{1}{6}\right)+\left(1-\dfrac{1}{12}\right)+...+\left(1-\dfrac{1}{90}\right)\\ =\left(1+1+1+1+1+1+1+1+1\right)-\left(\dfrac{1}{2}+\dfrac{1}{6}+...+\dfrac{1}{90}\right)\\ =9-\left(\dfrac{1}{1\cdot2}+\dfrac{1}{2\cdot3}+...+\dfrac{1}{9\cdot10}\right)\\ =9-\left(1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+...+\dfrac{1}{9}-\dfrac{1}{10}\right)\\ =9-\left(1-\dfrac{1}{10}\right)=9-\dfrac{9}{10}=\dfrac{81}{10}\)

81/10

8,1 nha

a) \(\frac{5}{6}+\frac{11}{12}+\frac{19}{20}+...+\frac{89}{90}\)

\(=1-\frac{1}{6}+1-\frac{1}{12}+...+1-\frac{1}{90}\)

\(=\left(1+1+1+...+1\right)-\left(\frac{1}{6}+\frac{1}{12}+...+\frac{1}{90}\right)\)

\(=\left(1+1+1+...+1\right)-\left(\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+...+\frac{1}{9\cdot10}\right)\)

Từ 2 đến 9 có : ( 9 - 2 ) / 1 + 1 = 8 ( số hạng ) => có 8 số 1

\(\Rightarrow8-\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{9}-\frac{1}{10}\right)\)

\(=8-\left(\frac{1}{2}-\frac{1}{10}\right)\)

\(=8-\frac{2}{5}=\frac{38}{5}\)

b) \(\frac{1}{2}+\frac{5}{6}+\frac{11}{12}+...+\frac{109}{110}\)

\(=1-\frac{1}{2}+1-\frac{1}{6}+...+1-\frac{1}{110}\)

\(=\left(1+1+1+...+1\right)-\left(\frac{1}{2}+\frac{1}{6}+...+\frac{1}{110}\right)\)

\(=\left(1+1+...+1\right)-\left(\frac{1}{1\cdot2}+\frac{1}{2\cdot3}+...+\frac{1}{10\cdot11}\right)\)

Từ 1 đến 10 có : ( 10 - 1 ) / 1 + 1 = 10 ( số hạng ) => có 10 số 1

\(\Rightarrow10-\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{10}-\frac{1}{11}\right)\)

\(=10-\left(1-\frac{1}{11}\right)\)

\(=10-\frac{10}{11}=\frac{100}{11}\)

100/11 nha

câu b bằng 891/110

câu a bằng 76/10

Đặt A = 11/12 + 19/20 + 29/30 + 41/42 + 55/56 + 71/72 + 89/90

A = 1 - 1/12 + 1 - 1/20 + 1 - 1/30 + 1 - 1/42 + 1 - 1/56 + 1 - 1/72 + 1 - 1/90

A = ( 1 + 1 + 1 + 1 + 1 + 1 + 1 ) - ( 1/12 + 1/20 + 1/30 + 1/42 + 1/56 + 1/72 + 1/90 )

A = 7 - 7/30

A = \(6\frac{23}{30}\)

203/30

Dịch ra là: Tìm chữ số cuối cùng của A = 11 x 21 x 31 x ...... x 71 + 9 x 19 x 29 x .... x 89

Giải: Ta thấy chữ số cuối của 11 x 21 x 31 x ...... x 71 là 1

Từ 9 đến 89 có (89 – 9) : 10 + 1 = 9 (thừa số) nên tích này có chữ số cuối cùng là 9.

(số thừa số lẻ).

Chữ số tận cùng của A là chữ số 0. (vì 1 + 9 = 10).

Nhớ k cho mình nhé!