標題:
Simplify、恆等式、percentage、ratio、map 20分 英文
發問:
15) 2^2n?9^n / 3^n = 16) If x = y-2x / 2y, then y = 17) If a(2x-x^2)+b(2x^2-x) ≡ -5x^2+4x, then a = 18) The marked price of a book is 20% above the cost. If the book is sold at a 10% discount on the marked price, then the percentage profit is 19) If (a-b):(b-2a) = 2:3, then a:b = 更新: 20) A box contains two kinds of coins:$5 and $2. The ratio of the number of $5 coins to the number of $2 coins is 4:5. If the total value of the coins is 490, then the total number of coins in the box is 更新 2: 21) The scale of a map is 1:20 000. If two buildings are 3.8 cm apart on the map, then the actual distance between the two buildings is 22) If (-2,3) is the mid-piont of (a,-1) and (4,b), then b = 更新 3: 有 step 一定要 show step，冇就直接寫答案，唔該晒 =]
最佳解答:
15) 2^2n X 9^n/3^n =2^2n X (3^2)^n/3^n =2^2n X 3^2n/3^n =2^2n X 3^n 16) x = y-2x / 2y 2xy=y-2x 2xy+2x=y 2x(y+1)=y x=y/[2(y+1)] 17) a(2x-x^2)+b(2x^2-x) ≡ -5x^2+4x (2b-a)x^2+(2a-b)x ≡ -5x^2+4x therefore, 2b-a=-5 --------(1) 2a-b=4 --------(2) (2)X2+(1) 3a=3 a=1 18) Let y be the cost y X 120% X 90% = 1.08y % of profit= (1.08y-y)/y X 100% = 8% 19) (a-b):(b-2a) = 2:3 (a-b)/(b-2a) = 2/3 3(a-b) = 2(b-2a) 3a-3b = 2b-4a 7a = 5b a/b = 5/7 a:b = 5:7 20) Let the no of $5 coins=x the no of $2 coins=y x/y=4/5 5x=4y on the other hand, 5x+2y=480 (i think you made a typing mistake of the $490) 4y+2y=480 6y=480 y=80 therefore, x=4/5y=64 total no of coins=80+64=144 (if the total value of coins = 490, then the ratio of the $5 coins to $2 coins will not be 4:5) 21) let d be the actual distance 1/20000=3.8/d d=76000cm 22) use the mid pt formula (-1+b)/2=3 b=7
Simplify、恆等式、percentage、ratio、map 20分 英文
發問:
15) 2^2n?9^n / 3^n = 16) If x = y-2x / 2y, then y = 17) If a(2x-x^2)+b(2x^2-x) ≡ -5x^2+4x, then a = 18) The marked price of a book is 20% above the cost. If the book is sold at a 10% discount on the marked price, then the percentage profit is 19) If (a-b):(b-2a) = 2:3, then a:b = 更新: 20) A box contains two kinds of coins:$5 and $2. The ratio of the number of $5 coins to the number of $2 coins is 4:5. If the total value of the coins is 490, then the total number of coins in the box is 更新 2: 21) The scale of a map is 1:20 000. If two buildings are 3.8 cm apart on the map, then the actual distance between the two buildings is 22) If (-2,3) is the mid-piont of (a,-1) and (4,b), then b = 更新 3: 有 step 一定要 show step，冇就直接寫答案，唔該晒 =]
最佳解答:
15) 2^2n X 9^n/3^n =2^2n X (3^2)^n/3^n =2^2n X 3^2n/3^n =2^2n X 3^n 16) x = y-2x / 2y 2xy=y-2x 2xy+2x=y 2x(y+1)=y x=y/[2(y+1)] 17) a(2x-x^2)+b(2x^2-x) ≡ -5x^2+4x (2b-a)x^2+(2a-b)x ≡ -5x^2+4x therefore, 2b-a=-5 --------(1) 2a-b=4 --------(2) (2)X2+(1) 3a=3 a=1 18) Let y be the cost y X 120% X 90% = 1.08y % of profit= (1.08y-y)/y X 100% = 8% 19) (a-b):(b-2a) = 2:3 (a-b)/(b-2a) = 2/3 3(a-b) = 2(b-2a) 3a-3b = 2b-4a 7a = 5b a/b = 5/7 a:b = 5:7 20) Let the no of $5 coins=x the no of $2 coins=y x/y=4/5 5x=4y on the other hand, 5x+2y=480 (i think you made a typing mistake of the $490) 4y+2y=480 6y=480 y=80 therefore, x=4/5y=64 total no of coins=80+64=144 (if the total value of coins = 490, then the ratio of the $5 coins to $2 coins will not be 4:5) 21) let d be the actual distance 1/20000=3.8/d d=76000cm 22) use the mid pt formula (-1+b)/2=3 b=7
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