Bài 18: Tính nhanh:
| $ \begin{array}{l}a.\,\,\,274+\left( {158+26} \right)\\c.\,\,\,3.125.121.8\\e.\,\,\,29+132+237+868+763\\g.\,\,\,25.5.4.31.2\\i.\,\,\,98.31+62\\l.\,\,\,28.\left( {231+69} \right)+72.\left( {60+240} \right)\\n.\,\,\,35.34+35.86+65.75+65.45\\p.\,\,\,10+11+12+13+…+99\end{array}$ | $ \begin{array}{l}b.\,\,\,123+132+321+312\\d.\,\,\,367+129+133+371+17\\f.\,\,\,652+327+148+15+73\\h.\,\,\,37.64+37.36\\k.\,\,\,4.7.76+28.24\\m.\,\,\,136.48+16.272+68.20.2\\o.\,\,\,3.25.8+4.37.6+2.38.12\\q.\,\,\,1+6+11+16+….+46+51\end{array}$ |
Bài 19: Tìm số tự nhiên x, biết:
a. $ \left( {x-45} \right).27=0$
b. $ 21.\left( {34-x} \right)=42$
c. $ 2x+3x=1505$
d. $ 0.\left( {5-x} \right)=0$
e. $ 1+35+…..+x=3200$ (x là số lẻ)
f. $ \left( {x+1} \right)+\left( {x+2} \right)+\left( {x+3} \right)+…+\left( {x+100} \right)=5750$
Bài 20: Không tính giá trị cụ thể, hãy so sánh hai biểu thức:
a) $ A=123.123\,\,\,v\grave{a}\,\,\,B=121.124$
b) $ C=123.137137\,\,\,v\grave{a}\,\,\,D=137.123123$
c) $ E=2015.2017\,\,v\grave{a}\,\,\,F=2016.2016$