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BA
21 tháng 10 2019
\(15+15\cdot2+7\cdot15-100\)
\(=15+30+105-100\)
\(=150-100\)
\(=50\)
21 tháng 10 2019
15 + 15 * 2 + 7 * 15 - 100
= 15 * ( 1+2+7) - 100
= 15*10-10*10
= (15-10) * 10
= 5 * 10
= 50
27 tháng 6 2015
1a, 15/10 = 1,5 , 675/10 = 67,5 , 7/10 = 0,7 , 79/100 = 0,79 , 5/100 = 0,05 , 67/100 = 0,67
1b, 1/2 = 5/10 = 0,5 ;
3/4 = 75/100 = 0,75
15/8 = 1875/1000 = 1,875
7/25 = 28/100 = 0,28
19/30 = 63,33
21/125 = 168/1000 = 0,168
l i k e
27 tháng 6 2015
a) \(\frac{15}{10}=1,5\) \(\frac{675}{10}=6,75\) \(\frac{7}{10}=0,7\)
\(\frac{79}{100}=0,79\) \(\frac{5}{100}=0,05\) \(\frac{67}{100}=0,67\)
b) \(\frac{1}{2}=1\div2=0,5\) \(\frac{3}{4}=3\div4=0,75\)
\(\frac{15}{8}=15\div8=1,875\) \(\frac{7}{25}=7\div25=0,28\)
\(\frac{19}{30}=19\div30=0,63\) \(\frac{21}{125}=21\div125=0,168\)
10 tháng 8 2022
1.3.77−1+3.7.99−3+7.9.1313−7+9.13.1515−9+\frac{19-13}{13.15.19}+13.15.1919−13
=\frac{1}{1.3}-\frac{1}{3.7}+\frac{1}{3.7}-\frac{1}{7.9}+\frac{1}{7.9}-\frac{1}{9.13}+\frac{1}{9.13}-\frac{1}{13.15}+\frac{1}{13.15}-\frac{1}{15.19}=1.31−3.71+3.71−7.91+7.91−9.131+9.131−13.151+13.151−15.191
=\frac{1}{1.3}-\frac{1}{15.19}=\frac{95}{285}-\frac{1}{285}=\frac{94}{285}=1.31−15.191=28595−2851=28594
b,=\frac{1}{6}.\left(\frac{6}{1.3.7}+\frac{6}{3.7.9}+\frac{6}{7.9.13}+\frac{6}{9.13.15}+\frac{6}{13.15.19}\right)b,=61.(1.3.76+3.7.96+7.9.136+9.13.156+13.15.196)
làm giống như trên
c,=\frac{1}{8}.\left(\frac{1}{1.2.3}+\frac{1}{2.3.4}+\frac{1}{3.4.5}+...+\frac{1}{48.49.50}\right)c,=81.(1.2.31+2.3.41+3.4.51+...+48.49.501)
=\frac{1}{16}.\left(\frac{2}{1.2.3}+\frac{2}{2.3.4}+\frac{2}{3.4.5}+...+\frac{2}{48.49.50}\right)=161.(1.2.32+2.3.42+3.4.52+...+48.49.502)
=\frac{1}{16}.\left(\frac{3-1}{1.2.3}+\frac{4-2}{2.3.4}+\frac{5-3}{3.4.5}+...+\frac{50-48}{48.49.50}\right)=161.(1.2.33−1+2.3.44−2+3.4.55−3+...+48.49.5050−48)
=\frac{1}{16}.\left(\frac{1}{1.2}-\frac{1}{2.3}+\frac{1}{2.3}-\frac{1}{3.4}+\frac{1}{3.4}-\frac{1}{4.5}+...+\frac{1}{48.49}-\frac{1}{49.50}\right)=161.(1.21−2.31+2.31−3.41+3.41−4.51+...+48.491−49.501)
=\frac{1}{16}.\left(\frac{1}{2}-\frac{1}{2450}\right)=\frac{1}{16}.\left(\frac{1225}{2450}-\frac{1}{2450}\right)=\frac{153}{4900}=161.(21−24501)=161.(24501225−24501)=4900153
d,=\frac{5}{7}.\left(\frac{7}{1.5.8}+\frac{7}{5.8.12}+\frac{7}{8.12.15}+...+\frac{7}{33.36.40}\right)d,=75.(1.5.87+5.8.127+8.12.157+...+33.36.407)
=\frac{5}{7}.\left(\frac{8-1}{1.5.8}+\frac{12-5}{5.8.12}+\frac{15-8}{8.12.15}+...+\frac{40-33}{33.36.40}\right)=75.(1.5.88−1+5.8.1212−5+8.12.1515−8+...+33.36.4040−33)
=\frac{5}{7}.\left(\frac{1}{1.5}-\frac{1}{5.8}+\frac{1}{5.8}-\frac{1}{8.12}+\frac{1}{8.12}-\frac{1}{12.15}+...+\frac{1}{33.36}-\frac{1}{36.40}\right)=75.(1.51−5.81+5.81−8.121+8.121−12.151+...+33.361−36.401)
=\frac{5}{7}.\left(\frac{1}{5}-\frac{1}{1440}\right)=\frac{5}{7}.\left(\frac{288}{1440}-\frac{1}{1440}\right)=\frac{41}{288}=75.(51−14401)=75.(1440288−14401)=28841
P/S: . là nhân nha
AM
1
11 tháng 9 2021
\(\dfrac{6}{8}=\dfrac{3}{4}=\dfrac{75}{100}\)
\(\dfrac{12}{15}=\dfrac{4}{5}=\dfrac{80}{100}\)
\(\dfrac{7}{28}=\dfrac{1}{4}=\dfrac{25}{100}\)
\(\dfrac{15}{6}=\dfrac{5}{2}=\dfrac{250}{100}\)
DP
1
15 + 15x2 +15x7 -100
= 15 x( 1+2+7) -100
= 15 x 10 -100
= 150 -100 = 50
15+15x2+15x7-100
=15x(1+2+7)-100
=15x10-100
=150-100
=50