a) Tìm x biết: x 20% + x : 25% – x: 0,5 + x = 4,9
b) Tính: ( 1 – 1/2 ) x ( 1 – 1/3 ) x ( 1 – 1/4 ) x….x ( 1 – 1/2017 ) x ( 1 – 1/2018 ).
a) Tìm x biết: x 20% + x : 25% – x: 0,5 + x = 4,9 b) Tính: ( 1 – 1/2 ) x ( 1 – 1/3 ) x ( 1 – 1/4 ) x….x ( 1 – 1/2017 ) x ( 1 – 1/2018 ).
By Isabelle
a) `x xx 20% + x : 25% – x : 0,5 + x = 4,9`
`x xx 1/5 + x : 1/4 – x : 1/2 + x = 4,9`
`x xx 1/5 + x. 4 – x .2 + x= 4,9`
`x xx( 1/5 + 4 -2 +1)= 4,9`
`x xx 16/5= 49/10`
`x= 49/10 : 16/5`
`x=49/10 xx 5/16`
`x=49/32`
b) `(1 -1/2) xx ( 1-1/3) xx ( 1-1/4) xx …. xx( 1 – 1/2018)`
`= (2/2 – 1/2) xx ( 3/3 – 1/3) xx ( 4/4 – 1/4) xx …xx( 2018/2018 – 1/2018)`
`= 1/2 xx 2/3 xx 3/4 xx …xx 2017/2018`
`= (1 xx 2 xx 3 xx…xx 2017)/(2 xx 3 xx 4 xx…xx2018)`
`= 1/2018`
Đáp án:
Giải thích các bước giải:
a) x × 20% + x : 25% – x: 0,5 + x = 4,9
x × 1/5 + (x ÷ 1/4) – (x ÷ 1/2) + x = 4,9
x × 1/5 + x × 4 – x ×2 + x = 49/10
x × (1/5 +4 -2 +1) = 49/10
x × ( 1/5 + 20/5 – 10/5 +5/5) = 49/10
x × 16/5 = 49/10
x = 49/10 ÷ 16/5
x = 49/10 × 5/16
x= 49/32
b) ( 1 – 1/2 ) x ( 1 – 1/3 ) x ( 1 – 1/4 ) x….x ( 1 – 1/2017 ) x ( 1 – 1/2018 ).
= 1/2 × 2/3 × 3/4 ×…..× 2016/2017 × 2017/2018
= 1×2×3×…..×2017/2×3×4×…..×2018
= 1/2018
Nocopy
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