Solve math problems. Tomorrow, the teacher will give this kind of test. Please help me solve it. It takes a process, otherwise I won't understand what it means.

First, solve the problem.

1. 30% discount for one book, cheap 18 yuan. What is the original price? Formula:18/(1-0.7) =18/0.3 = 60, and the original price is 60.

The purchase price of 2.50 yuan for a piece of clothing increased by 10% at first, but decreased by 10% because of poor sales. Did you lose money? If so, how much did you lose? If so, how much did you earn? 50-50 * ( 1+ 10%) * ( 1- 10%) = 50-50 * 1. 1 * 0.9 = 50-55 * 09 = 50.

3. Car A has walked 40% of the whole journey from A to B, and it is 54 kilometers away from the midpoint. Find the distance between A and B: 54/(50%-40%) * 2 = 54/10% * 2 = 540 * 2 =1080 (km).

A pile of sand weighs 300 tons, 30% was transported for the first time, 25% for the second time, and the rest was transported for the third time. How many tons were shipped for the third time? Formula: 300 * (1-30%-25%) = 300 * 45% =135 (ton)

A road has been built for 240 meters, which is exactly 20% of this road. How many meters is the total length of the road, and how many meters have not been repaired? 240/20%-240 =1200-240 = 960 (m). Answer, this road has 1200m, and 960m has not been repaired.

Second, the calculation (can be simplified)

7/9÷[( 1/3+ 1/4)×4]=7/9 ÷[(4/ 12+3/ 12)×4]= 7/9÷[7/ 12×4]= 7/9÷[7/3]= 7/9*3/7]= 1/3 (5/8+37.5%)÷(2 1/ 10-209%)=(62.5%+37.5%)÷(2 10%-209%)= 1÷ 1%= 100

( 19/40+38)÷ 19

=( 19/40+ 1520/40)÷ 19

= 1539/40÷ 19

=2.025

7/20÷[(5/6-2/3)×3]

=7/20÷[(5/6-4/6)×3]

=7/20÷[ 1/6×3]

=7/20÷ 1/2

=7/20*2

=7/ 10