The opposite number of A-B is () A. a+bB. -（a+b）C. b-aD. -a-b

The opposite number of A-B is () A. a+bB. -（a+b）C. b-aD. -a-b

The number opposite to A-B is - (a-b) = b-a

There are 41 trees from the beginning to the end on one side of the road. The distance between the two trees is 2 meters. Now we need to install a street lamp every 20 meters on the other side of the road. How many lamps are installed? (both ends to be installed)

2 × (41-1) △ 20 + 1, = 2 × 40 △ 20 + 1, = 4 + 1, = 5 (lamps). Answer: five lamps are installed

The front view and the side view (left view) of an opaque cone are two congruent equilateral triangles. If the cone is placed upside down on the desktop, the forward projection of the cone on the horizontal desktop can not be ()
A. Circular area B. the area enclosed by the two waists and the half ellipse of isosceles triangle C. the area enclosed by the two waists and the half circle of isosceles triangle D. the oval area

Observe the four options, know that the cone on the desktop from the vertical position down to the horizontal position of the process (including the starting position and the final position), it can not be in the horizontal desktop orthographic projection is C, because if the cone projection is semicircle, the diameter of the projection circle is the same as the real diameter

A math problem, please explain clearly!
The road between city a and city B is 360 kilometers long. Xiao Wang drives from city a to city B by himself. Before he starts, he goes to the gas station to fill up a tank of gas. After 200 kilometers, he looks at the fuel meter and finds that there is still four fifths of the fuel in the tank. Please help him to calculate. If he doesn't fill up on the way, can he drive to city B?

The road between city a and city B is 360 kilometers long. Xiao Wang drives from city a to city B by himself. Before he starts, he goes to the gas station to fill up a tank of gas. After 200 kilometers, he looks at the fuel meter and finds that there is still four fifths of the fuel in the tank. Please help him to calculate. If he doesn't fill up on the way, can he drive to city B?
200÷（1-4/5）
=200÷1/5
=1000 km
Because: 1000 km ＞ 360 km
So: he can drive to city B

When two positive integers are divided, the quotient is 7 and the remainder is 5. If the divisor and the divisor are expanded to 4 times of the original, then the sum of the divisor, the divisor, the quotient and the remainder is 1039______ The divisor is______ ．

Let the divisor after expansion be & nbsp; X, the divisor be & nbsp; 4x + 20, x + 7x + 4 × 5 + 7 + 4 × 5 = 1039 & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; 8x = 992 & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & n

Wahaha, the price of each bottle of mineral water is 1.2 yuan. Now a and B stores offer preferential policies: 10% off for all stores, and 20% off for more than 20 bottles in B store

Mineral water can be preserved without deterioration, and water is drunk every day, so consider shopping mall B to buy

In order to find out the two light balls, they were weighed three times with a balance. The results are as follows: the first time: ① + ② is heavier than ③ + ④; the second time: ⑤ + ⑥ is lighter than ⑦ + Ⅷ; the third time: ① + ③ + ⑤ is as heavy as ② + ④ + Ⅷ. The two light balls are ()
A. ①、④B. ③、⑧C. ②、⑤D. ④、⑤

Because ① + ② is heavier than ③ + ④, there is at least one light ball in ③ and ④. Because ⑤ + ⑥ is lighter than ⑦ + Ⅷ, there is at least one light ball in ⑤ and ⑥. Because ① + ③ + ⑤ and ② + ④ + Ⅷ are the same weight, we can know that the number of the two light balls is ④ and ⑤

There are 8 bottles of mineral water, the number is 1 ~ 8, of which 6 bottles are the same weight, are qualified products, and the other 2 bottles are light, are unqualified products, weighed three times with the balance, the results are as follows
Next: for the first time, 1 + 2 is heavier than 3 + 4; for the second time, 5 + 6 is lighter than 7 + 8; for the third time, 1 + 3 + 5 is heavier than 2 + 4 + 8?

4 and 6
1+2>3+4
There are 1 and 2 qualified products
5+62+4+8
Describe qualified products 1, 3 and 5
All in all, 1, 2, 3, 5, 7 and 8 are qualified products
Unqualified products are 4 and 6

In order to find out the two light balls, they were weighed three times with a balance. The results are as follows: the first time: ① + ② is heavier than ③ + ④; the second time: ⑤ + ⑥ is lighter than ⑦ + Ⅷ; the third time: ① + ③ + ⑤ is as heavy as ② + ④ + Ⅷ. The two light balls are ()
A. ①、④B. ③、⑧C. ②、⑤D. ④、⑤

Because ① + ② is heavier than ③ + ④, there is at least one light ball in ③ and ④. Because ⑤ + ⑥ is lighter than ⑦ + Ⅷ, there is at least one light ball in ⑤ and ⑥. Because ① + ③ + ⑤ and ② + ④ + Ⅷ are the same weight, we can know that the number of the two light balls is ④ and ⑤

Master Wang produced a batch of parts, and the unqualified products were one nineteenth of the qualified products. Later, he found two unqualified products from the qualified products
Calculate the product pass rate of 94%, ask pass?
Change 94% to 94%

Master Wang produced a batch of parts, and the unqualified products were one nineteenth of the qualified products. Later, he found two unqualified products from the qualified products. At this time, he calculated the qualified rate of 94%. How many qualified products are there?
All products are unit 1
Then unqualified products account for 1 / 20 of the total
Later, it accounted for 1-94% = 6% = 3 / 50
All products have 2 / (3 / 50-1 / 20) = 2 / (1 / 100) = 200
There are 200 × 94% = 188 qualified products