速算問題　急~~

1. 375x32x25x13
=375x(8x4)x25x13
=(375x8)x(4x25)x13
=3000x100x13
=300000x13
=13x3x100000
=39x100000
=3900000

2. 78x35+65x39x2
=78x35+65x(39x2)
=78x35+65x78
=78x(35+65)
=78x100
=7800

3. 198x199199-199x198198
=198x(199x1001)-199x(198x1001)
=198x199x1001-199x198x1001
=0


4.
1 3 1
4--- - 1--- + 2---
2 4 3



6 4 9
= 4 --- + 2 --- - 1---
12 12 12

1
= 5 ---
12

1. 375x32x25x13
=375x25x32x13
=9375x32x13
=300000x13
=3900000

2. 78x35+65x39x2
=35+65x2x39x78
=100x2x39x78
=200x39x78
=78x78補00
=6084補00
=608400

3. 198x199199-199x198198
=(200-2)x(199200-1)-(200-1)x(198200-2)
=200-200x(199200-1)x(198200-2)
=1992x1982補0000+200-200-199200-(198200+198200)
=1992x1982補0000+200-200-199200-396400
=39481440000+200-200-199200-396400
=39481440000+0-199200-396400
=39481440000-199200-396400
=39481230800-396400
=39480844400

4.4--- -1--- + 2---
=4000-1000+2000
=3000+2000
=5000

2007-12-31 17:29:54 補充：
1=5--- 12

1. 375x32x25x13 3900000

2. 78x35+65x39x2 7800

3. 198x199199-199x198198 0

4.?