The price of each pair is 15% higher than the purchase price, and the price = (1+15%) x =1.15x.

If all of them are sold, the profit will be 120 yuan and the number of sandals will be120/(1.15x-x).

Only 80 pairs are sold, so 64 yuan is the only cost.

80* 1. 15x+64= number of sandals * x =120x/(1.15x-x).

x=8

2. Solution: Let the train be s meters long, the train speed be V, and the speed of Party A and Party B be V..

It took 6 seconds for the train to pass through A and 5 seconds for the train to pass through B.

(V car -v)*6=s, (V car+V) * 5 = S.

V car = 1 1v

Four minutes later, the train passes through B again, and the remaining distance is =4*60*V Train-4 * 60 * V = 2,400 V (the train goes and goes).

Time = 2400 volts /(v+v)= 1200 seconds =20 minutes.

3. Let * * have x pages.

Read the whole book, 15% is missing 4 pages. I saw 15%x-4 on the first day.

Residual =x-( 15%x-4)=0.85x+4.

The ratio of the number of pages read to the remaining pages is 1: 7.

( 15% x-4)/(0.85 x+4)= 1/7

x= 160