B4 : Tính bằng cách thuận tiện
a, 164/468 x 432/984 x 435/164 x 328/435
b , 14/5 + 17/3 + 19/3 - 8/9 + 17/9 - 4/5
c, ( 1-1/2 ) x ( 1-1/3 ) x ( 1-1/4 ) x ( 1-1/5 ) x ( 1-1/6 ) x ( 1-1/7 )
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b, 14/5 + 17/3 + 19/3 - 8/9 + 17/9 - 4/5
= ( 14/5 - 4/5 ) + ( 19/3 + 17/3 ) - ( 17/9 - 8/9 )
= 10/5 + 36/3 - 9/9 = 2 + 12 - 1 = 13
c, ( 1 - 1/2 ) x ( 1 - 1/3 ) x ( 1 - 1/4 ) x ( 1 - 1/5 ) x ( 1 - 1/6 ) x ( 1 - 1/7 )
= ( 2/2 - 1/2 ) x ( 3/3 - 1/3 ) x ( 4/4 - 1/4 ) x ( 5/5 - 1/5 ) x ( 6/6 - 1/6 ) x ( 7/7 - 1/7 )
= 1/2 x 2/3 x 3/4 x 4/5 x 5/6 x 6/7 = 1/7
b, 14/5 + 17/3 + 19/3 - 8/9 + 17/9 - 4/5
= ( 14/5 - 4/5 ) + ( 19/3 + 17/3 ) - ( 17/9 - 8/9 )
= 10/5 + 36/3 - 9/9 = 2 + 12 - 1 = 13
c, ( 1 - 1/2 ) x ( 1 - 1/3 ) x ( 1 - 1/4 ) x ( 1 - 1/5 ) x ( 1 - 1/6 ) x ( 1 - 1/7 )
= ( 2/2 - 1/2 ) x ( 3/3 - 1/3 ) x ( 4/4 - 1/4 ) x ( 5/5 - 1/5 ) x ( 6/6 - 1/6 ) x ( 7/7 - 1/7 )
= 1/2 x 2/3 x 3/4 x 4/5 x 5/6 x 6/7 = 1/7
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