Re: [計量] 好幾題數學問題 part 2
: 1. The sum of two numbers that differ by 1 is t. In terms of t, what is the
: value of the greather of the two numbers?
: ANS: t+1/2
題目意思是：
有兩個加起來為t的數，彼此相差1(differ by 1)，那麼這兩個數當然就分別為
t-1/2 和 t+1/2，so the greater one is t+1/2
: 2. A store charges $28 for a certain type of sweater. This price is 40 percent
: more than the amount it costs the store to buy one of these sweaters. At an
: end-of-season sale, store employee can purchase any remaining sweater at 30
: percent off the store's cost. How much would it cost an employee to
: perchase a sweater of this type at this sale?
: ANS: $14.00 我不了解這題目的意思百分之四十那部分我不懂題目表是的意思
意思是：28元這價格比成本多40%，所以推知成本為20元；
季末出清時員工可以用比成本低三成的錢買入，故要花 20*0.7 = 14元
: 3. If 10^50-74 is written as an integer in base 10 notation, what is the sum
: of the digits in that integer?
: ANS: 440
the sum of digits 是指每位數的數字的總合，例如99的sum of digits=9+9=18
回到題目，10^54-74 = 999....9926
^^^^^^^^^<==共48個9
所以sum of digits = 48*9 + 2 + 6 = 440
: 4. 看不懂題目的意思
: Each signal that a certain ship can make is composed of 3 different flags
: hanging vertically in a particular order. How many unique signals can be
: made by using 4 different flags?
: ANS: 24
一個訊號係由3種不同的旗子排列組合而成，現有4種不同的旗子可以拿來用。
但是儘管有4種能用還是必須先挑出3種，再由這3種去排列，
所以組合數為：C[4,3] * 3! = 4*6 =24
: 5.這題我想問有沒有比較快速的方法或是絕竅
: The value of (9 x 10^7)(9 x 10^8) is closest to which of the following?
: ANS: 10^17
(9*10^7)(9*10^8) = 81*10^15 = 8.1*10^16 approxly smaller than 10^17
: 6. If x > 0, then 1/ (√2x +√x) =
: ANS: √2-1 / √X 這類型題目相當不擅長,請問這要怎麼改進 @@ 幾乎每次都會算錯
: 再次謝謝各位版友 ^^
其實就是先把根號x在分母提出來，剩下的工作就只是開始化簡 1/(√2+1)
1/(√2+1) = (√2-1)/(√2+1)(√2-1) = (√2-1)/(2-1) =(√2-1)，完畢。
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03/29 12:21, , 1F
03/29 12:21, 1F
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