Recent content by fork

Hello, everybody, I know how to get the first step, but I don't know how can the first step be changed to the format of the final answer, can anyone help? Thanks.:smile:

Four lattices are selected from 5*4 grid board indicated in the figure above so that they form the corners of a rectangle having sides parallel to the edges of the board. How many different rectangles can be formed in this way? Can anyone give me some clues to answer this question? Thanks:approve:

I know how to do it now. a)5C4+5C3+5C2 b)5C4 x4!+5C3 x4!+5C2 x4!/2! right? Thanks.

If 4 letters are selected from the 7 letters of the word "WINDOWS", calculate the number of possible a)combinations. b)arrangemants. I have got the answer but I still don't understand how to calculate it. Thanks.:rolleyes:

I don't understand how can I set up D_{n+1} = D_n + n - 2.

Find the number of diagonals that can be drawn in an n-side polygon. The answer is n(n-3)/2. I don't know how to do that.

The answer from a1 to b are 2520, 840 and 360 respectively. I don't know how to obtain the result from the above counting. Thanks for your answering. Also, are there any quicker methods of doing this question?

The prime ministers A, B, C, D, E, F and G of 7 countries will address at a summer meeting. a) Find the number of arrangerments that can be made so that 1)A will speak before C, 2)A will speak before C and C will speak before E. b)In how many of those ways in a2) will C speak immediately...

Actually, I don't understand the above steps, why we have to add 852? I am sorry that I am too stupid. Also, should it be 6*5*4? :confused: Thanks for your answering. ^_^

a)How many different numbers of 4 digits may be formed with the dgits 0,1,2,5,6,7,8 if no digit is used more than once in any number? b)Find the sum of all he numbers formed in (a). I know how to do the part a), but I'm totally stump when I see part b). Thanks.

Describe the energy changes involved when the vehicle is accelerating along the horizontal road. I don't know what are the energy changes during the process. Thanks.

In the figure, A, B and C are the centres of three equal circles, each of radius 1 cm. Find the area of the shaded region. I feel stump with this question. Thanks

In fact, the ans is 2:5. And I can calculate this question by using your method. Thank.

In the figure, ABCD is a rectangle. M is the midpoint of BC and AC intersects MD at N. Find the Area of the NCD: Area of ABMN. I am sorry i don't know how to solve this question. Thanks.

O, I forgot there is a rule called " cosine rule" in the world, thanks.