99-97+95-93+91-89+...+7-5+3-1
Số các số hạng là:
(99-1):2+1=50 số
=(99-97)+(95-93)+(91-89)+...+(7-5)+(3-1)
Số cặp sẽ là:
50:2=25 cặp
=2+2+2+...+2+2
=2x25
=50
32x47+32-53+168+79+132
=1504+32-53+(168+79+132)
=1536-53+379
=1483+379
=1862
25/2+25/3-25/7/1/3+1/3-1/7
\(=\frac{25}{2}+\frac{25}{3}-\frac{25}{7}:\frac{1}{3}+\frac{1}{3}-\frac{1}{7}\)
\(=\frac{25}{2}+\frac{25}{3}-\frac{25}{7}\times\frac{3}{1}+\frac{1}{3}-\frac{1}{7}\)
\(=\frac{25}{2}+\frac{25}{3}-\frac{156}{7}+\frac{1}{3}-\frac{1}{7}\)
\(=\frac{525}{42}+\frac{350}{42}-\frac{936}{42}+\frac{14}{42}-\frac{6}{42}\)
\(=\frac{875}{42}-\frac{936}{42}+\frac{14}{42}-\frac{6}{42}\)
\(=\frac{-61}{42}+\frac{14}{42}-\frac{6}{42}\)
\(=\frac{-47}{42}-\frac{6}{42}\)
\(=\frac{-53}{42}\)
( Chú Ý: lớp 5 chưa học số âm )
