Question

19/17×14+3/17×19/12

8道脱式计算,
3/2×5+3/5×8+3/8×11+……+3/20×23
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4/5×2/9+4/5×7/9-4/5
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48×（7/12+1/2-1)
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36×（17/18-2/9)
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53×19/52
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4/13×3/7+3/14×4/7
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9/20×399+9/20
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7/12-9/20+11/30-13/42+15/56-17/72
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Answer 1

3/2×5+3/5×8+3/8×11+……+3/20×23
=1/2-1/5+1/5-1/8+1/8-1/11+...+1/20-1/23
=1/2-1/23
=23-2/46
=21/46
4/5×2/9+4/5×7/9-4/5
=4/5×(2/9+7/9)-4/5
=4/5×1-4/5
=4/5-4/5
=0
48×（7/12+1/2-1)
= 48×7/12+48×1/2-48×1
=28+24-48
=4
36×（17/18-2/9)
= 36×17/18- 36×2/9
=34-18
=16
53×19/52
= (52+1)×19/52
=52×19/52+1×19/52
=19+19/52
=19又19/52
4/13×3/7+3/14×4/7
= 3/13×4/7+3/14×4/7
=（1/13+1/14）×12/7
=(13+14/182)×12/7
=(27/182)×12/7
=162/637
9/20×399+9/20
=9/20×(399+1)
=9/20×400
=180
7/12-9/20+11/30-13/42+15/56-17/72
= (1/3+1/4)-(1/4+1/5)+(1/5+1/6)-(1/6+1/7)+(1/7+1/8)-(1/8+1/9)
= 1/3+1/4-1/4-1/5+1/5+1/6-1/6-1/7+1/7+1/8-1/8-1/9
= 1/3-1/9
=2/9