2. There are four cards with the same back, A, B, C and D, among which four different geometric figures (A, triangle; B, circle; C, parallelogram; D, regular Pentagon), Xiaohua washes the back of these four cards and then draws out one card, puts it back and washes it and then draws out another card, and uses the list method to represent all possible results of the contact between the two cards (which can be represented by A, B, C and D).
Answer: 6- 1=5 (times)
30/5=6 (seconds)
12-1=11(times)
1 1*6=66 (seconds)
A: The bell will last for 66 seconds.
Note: 1: It rang six times, with five intervals. 1-2 2-3 3-4 4-5 5-6, with five intervals.
So it rings once every 6 seconds.
(2)aa ab ac ad
bb ba bc bd
cc ca cb cd
dd da db dc
So a * * * has 16 kinds.
A store will increase the purchase price of a DVD by 35%, then give a 10% discount to the guests and send the taxi fare to 50 yuan.
As a result, each DVD still earns 208 yuan, so what is the pricing of each DVD?
Solution: Let the purchase price of DVD be X yuan.
( 1+35%)X*90%—50=X+208
1.2 15X-50=X+208
0.2 15X=258
X= 1200
1200 * (1+35%) * 90% =1620 (yuan)
A: The unit price of each DVD is 1620 yuan.
A project must be completed within the specified time. If the number of employees decreases by 6, the working hours will increase by 12 days. If the number of employees increases by 4, the working hours will be reduced by 4 days. Try to find the stipulated time and the original number of people? (Solution of binary linear equation, whole process)
Let the original number of people be x and the specified time be y.
(X-6)(Y+ 12)=XY
(X+4)(Y-4)=XY
x= 16
y=20
Given that A-B = 3 and B-C = 2, find the value of A+B+C-AB-BC-AC (representing the square.
(a-b)+(b-c)=a-c=3+2=5
a⒉+b⒉+c⒉-ab-bc-ac=a(a-b)+b(b-c)+c(c-a)
=3a+2b-5c
=(3a-3c)+(2b-2c)
=3(a-c)+2(b-c)
= 15+4
= 19
Five questions