# 數學習題(幫幫我^^)以下的數學問題麻煩附上算式唷!謝謝

1. A woman can do a certain job in 10 hours and her younger daughter can do it in 12 hours. After the woman and her younger daughter have been working for 1 hour, they are joined by the older daughter, and the 3 complete the job in 3 more hours. How long will it take the older daughter alone do the job by herself?

2. Two printing presses are available to print the daily college newspaper. If only one press is used, it takes the older press twice as long to print an edition as it takes the newer press. If the two presses together can print an edition in 3 hours, how long would it take each press alone to print an edition?

3. One secretary can do a particular typing job in 6 hours and another secretary can do the same job in 4 hours. How long would it take if job is done by two secretaries working together?

### 2 個解答

• 1 0 年前
最佳解答

1. A woman can do a certain job in 10 hours and her younger daughter can do it in 12 hours. After the woman and her younger daughter have been working for 1 hour, they are joined by the older daughter, and the 3 complete the job in 3 more hours. How long will it take the older daughter alone do the job by herself?

Set the woman to be W, younger daughter D1, and older one D2, total

work as Wt.

W x 10 = D1 x 12 = Wt------------------------------------ 1

Wt - (W+D1) x 1 = (W+D1+D2) x 3--------------------2

Plug equation 1 to equation 2, then we will get:

Wt - 0.1Wt - 0.0833Wt = (0.1Wt + 0.0833Wt + D2) x 3

simplify~ Wt- 0.1Wt-0.0833Wt-0.3Wt-0.25Wt = 3D

0.26667= 3D So Wt= 11.25

Ans: 11.25 hours~

2. Two printing presses are available to print the daily college newspaper. If only one press is used, it takes the older press twice as long to print an edition as it takes the newer press. If the two presses together can print an edition in 3 hours, how long would it take each press alone to print an edition?

Set total work to be Wt, new process A and the old one is B

known: Wt= (A+B) x 3---------------1

A=2B--------------------------2

first, plug in equation 1 with A form:

and we got ~ Wt=(A+0.5A) x 3, Wt= 4.5 A

Ans: takes new process 3 hours

Plug in equation 2 with B form:

And we got ~ Wt=(2B+B) x 3, Wt= 9B

Ans: takes old process 9 hours

3. One secretary can do a particular typing job in 6 hours and another secretary can do the same job in 4 hours. How long would it take if job is done by two secretaries working together?

Set total work to be Wt, and A, B respect to eahc secretary

Known: Wt=6A----------------------1

Wt=4B----------------------2

so A=0.1666667Wt, B=0.25Wt

Wt / (0.166667Wt+0.25Wt)= 2.4

Ans: 2.4 Hours!!!!

隨便算了 一下, 你先把答案代進去看看.....要去吃晚飯沒時間幫你驗算....有錯的話我再幫你改....先掰囉

參考資料： 自己
• 匿名使用者
1 0 年前

你最好分兩次問, 英文可以數學超不行