標題:
maths.F.2(before 10:00 tonight)
發問:
1. tom is 3 times as old as his sister. if the difference of their ages is 36, find the ages of tom and his sister. 2.if both the numerator and denominator of a fraction increase by 1, the value of the fraction becomes 1/2. if each of them decrease by 1, the value of the fraction becomes 1/4. find the fraction.
最佳解答:
1.Let his sister ages y...then tom ages 3y the difference of their ages is 36.. 3y-y=36 2y=36 y=18 his sister ages 18...then tom ages 54(呢題有d怪..maybe我理解錯個題目) 2.if both the numerator and denominator of a fraction increase by 1, the value of the fraction becomes 1/2. if each of them decrease by 1, the value of the fraction becomes 1/4. find the fraction. let the numerator be y.. denominator be z (y+1)/(z+1)=1/2...(1) (y-1)/(z-1)=1/4....(2) In (1) 2(y+1)=z+1 2y+2=z+1 z=2y+1..(3) Sub (3) into (2) (y-1)/[(2y+1)-1)=1/4 4(y-1)=2y 4y-2y=4 y=2..(4) Sub (4) into (3) z=2x2+1 z=5 so the fraction is 2/5 2007-12-17 22:35:04 補充： 第一條一定不是9和27..因為 difference of their ages 不是36
1. Let Tom's sister be x years old, then Tom will be 3x years old, so 3x - x = 36 gives x = 18 and 3x = 54 Therefore Tom is 54 and his sister is 18. 2. Let x be the numerator and y be the denominator, Thus (x+1)(y+1) =1/2 gives 2(x+1) = y+1 or y = 2x + 1 and (x-1)/(y-1) = 1/4 gives 4(x-1) = y - 1 or y= 4x - 3 so y = 2x + 1 = 4x - 3 gives 2x = 4 or x = 2 so y = 2x +1 =2(2) + 1 = 5 so the fraction is 2/5|||||Let x be tom's sister ages 3x-x=36 2x=18 x=9 so that Tom's sister age is 9 tom is 27|||||chunwai320 但散 Y ??? 3y-y =36 2y=18 (為什麼是 18) 2y=36 ???? y=9 2007-12-17 22:34:07 補充： y=18|||||1.. let T be Tom 's sister's age 3T-T=36 2T=36 T=18 Tom is 54 and his sister is 18# 第二題我記得我做過 但我唔記得左點solve/___\|||||1. Let Tom's age be x, his sister's age be y, x=3y ---(1) x-y=36 ---(2) Put (1) into (2), 3y-y =36 2y=18 y=9 ---(3) Put (3) into (1), x=27 Ages of tom is 27 Ages of his sister is 9 2. Let numerator and denominator of a fraction be (x/y), (x+1)/(y+1) = 1/2 2x+2=y+1 2x-y+1=0 ---(1) (x-1)/(y-1) = 1/4 4x-4=y-1 4x-y-3=0 ---(2) (2)-(1): 2x-4=0 x=2 ---(3) Put (3) into (1): 2(2)-y+1=0 y=5 Therefore, the fraction is (2/5)|||||1. Let x be tom's sister ages 3x-x=36 2x=18 x=9 so that Tom's sister age is 9 tom is 27 唔知幫唔幫到你,第2條好難解= =
maths.F.2(before 10:00 tonight)
發問:
1. tom is 3 times as old as his sister. if the difference of their ages is 36, find the ages of tom and his sister. 2.if both the numerator and denominator of a fraction increase by 1, the value of the fraction becomes 1/2. if each of them decrease by 1, the value of the fraction becomes 1/4. find the fraction.
最佳解答:
1.Let his sister ages y...then tom ages 3y the difference of their ages is 36.. 3y-y=36 2y=36 y=18 his sister ages 18...then tom ages 54(呢題有d怪..maybe我理解錯個題目) 2.if both the numerator and denominator of a fraction increase by 1, the value of the fraction becomes 1/2. if each of them decrease by 1, the value of the fraction becomes 1/4. find the fraction. let the numerator be y.. denominator be z (y+1)/(z+1)=1/2...(1) (y-1)/(z-1)=1/4....(2) In (1) 2(y+1)=z+1 2y+2=z+1 z=2y+1..(3) Sub (3) into (2) (y-1)/[(2y+1)-1)=1/4 4(y-1)=2y 4y-2y=4 y=2..(4) Sub (4) into (3) z=2x2+1 z=5 so the fraction is 2/5 2007-12-17 22:35:04 補充： 第一條一定不是9和27..因為 difference of their ages 不是36
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其他解答:1. Let Tom's sister be x years old, then Tom will be 3x years old, so 3x - x = 36 gives x = 18 and 3x = 54 Therefore Tom is 54 and his sister is 18. 2. Let x be the numerator and y be the denominator, Thus (x+1)(y+1) =1/2 gives 2(x+1) = y+1 or y = 2x + 1 and (x-1)/(y-1) = 1/4 gives 4(x-1) = y - 1 or y= 4x - 3 so y = 2x + 1 = 4x - 3 gives 2x = 4 or x = 2 so y = 2x +1 =2(2) + 1 = 5 so the fraction is 2/5|||||Let x be tom's sister ages 3x-x=36 2x=18 x=9 so that Tom's sister age is 9 tom is 27|||||chunwai320 但散 Y ??? 3y-y =36 2y=18 (為什麼是 18) 2y=36 ???? y=9 2007-12-17 22:34:07 補充： y=18|||||1.. let T be Tom 's sister's age 3T-T=36 2T=36 T=18 Tom is 54 and his sister is 18# 第二題我記得我做過 但我唔記得左點solve/___\|||||1. Let Tom's age be x, his sister's age be y, x=3y ---(1) x-y=36 ---(2) Put (1) into (2), 3y-y =36 2y=18 y=9 ---(3) Put (3) into (1), x=27 Ages of tom is 27 Ages of his sister is 9 2. Let numerator and denominator of a fraction be (x/y), (x+1)/(y+1) = 1/2 2x+2=y+1 2x-y+1=0 ---(1) (x-1)/(y-1) = 1/4 4x-4=y-1 4x-y-3=0 ---(2) (2)-(1): 2x-4=0 x=2 ---(3) Put (3) into (1): 2(2)-y+1=0 y=5 Therefore, the fraction is (2/5)|||||1. Let x be tom's sister ages 3x-x=36 2x=18 x=9 so that Tom's sister age is 9 tom is 27 唔知幫唔幫到你,第2條好難解= =
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