The mathematics interest group held a test. There were 15 questions in the whole paper. It was stipulated that 8 points would be deducted for each right question and 4 points would be deducted for each wrong question. Xiaoying got 72 points in total, and she did it right______ Question

The mathematics interest group held a test. There were 15 questions in the whole paper. It was stipulated that 8 points would be deducted for each right question and 4 points would be deducted for each wrong question. Xiaoying got 72 points in total, and she did it right______ Question

The wrong questions are: (8 × 15-72) △ 8 + 4, = (120-72) △ 12, = 48 △ 12, = 4 (DAO); he did right: 15-4 = 11 (DAO); a: he did right 11 questions. So the answer is: 11

Xiao Ming did 20 math problems, and 3 points were deducted for one wrong problem. As a result, Xiao Ming got 60 points. How many problems did Xiao Ming do right?

I did 15 questions right and 5 questions wrong

The passenger car and the freight car leave each other at the same time from a and B, and meet five hours later. After meeting, the two cars are still moving at the same speed, when they are 196 km apart
80% of the total distance traveled by freight cars, and the ratio of the distance traveled by passenger cars to the distance not traveled is 3:2

The ratio of the distance traveled and the distance not traveled is 3:2
It shows that the whole journey of the bus: 3 / (3 + 2) = 3 / 5
Then the two cars travel the whole journey: 80% + 3 / 5 = 7 / 5
Because the two cars travel 1 / 5 of the whole journey per hour
Then: the line time is: 75 / △ 1 / 5 = 7 hours
The distance is 196 × 5 / (7-5) = 490 km
Or:
It shows that the whole journey of the bus: 3 / (3 + 2) = 3 / 5
Then the two cars travel the whole journey: 80% + 3 / 5 = 7 / 5
Then the distance between the two cars is 7 / 5-1 = 2 / 5
Distance: 196 △ 2 / 5 = 490km

The sum of the reciprocal of natural number a and B is 20 out of 91. What are the two natural numbers?

Because 91 = 7 * 13, 7 and 13 are coprime
So these two numbers are 7 and 13

Factorization: A ^ 4 - (5a + b) ^ 2

a^4-(5a+b)^2=(a²+5a+b)(a²-5a-b)

The store shipped 480KG of oranges, apples and pears. The weight of oranges is 5 / 6 of that of apples, and that of pears is 3 / 10 of that of apples. How many kg of each of the three kinds of fruits?

Apple:
480 / (5 / 6 + 1 + 3 / 10) = 225 kg
a mandarin orange:
225 * 5 / 6 = 187.5kg
Pear:
225 * 3 / 10 = 67.5kg

12 of a number is 90 more than 13. This number is______ ．

90 (12-13) = 90 (16) = 540. A: the number is 540. So the answer is: 540

Unit conversion of mass
The mass of the moon is about 7.4 x 10 to the 21st power, tons = [] kg = [] G
The mass of the chlorine atom is 1.7 x 10 to the minus 27th power, kg = [] ton = [] mg

7.4×1021t=7.4×1024kg=7.4×1027g
1.7×10-27kg=1.7×10-30t=1.7×10-21mg

The fruit shop brought in a batch of apples. One third of them were sold on the first day, and 25% on the second day. There were 110 kilograms left. How many kilograms of these apples are there?

110 ÷ (1-1 / 3-25%) = 264 kg

1 / 2, 1 / 3, 1 / 4, 1 / 9, 1 / 8, 1 / 27 ()

1/16,1/81