1÷4×( 1+60%)=0.4 yuan.
2. A book is priced in 30 yuan, and the book is sold at a 20% discount. The profit rate is 20%, and the book costs (20) yuan.
30×0.8( 1+20%)= 20 yuan.
3. Shopping malls buy a batch of TVs, and initially set the price at a profit rate of 25%. In order to speed up the capital turnover, the sales price is reduced by 10%, and each unit will make a profit in 250 yuan after the price reduction. The purchase price of each TV is (2000) yuan.
250 ÷ (125% × 90%-1) = 2000 yuan.
4. Dissolve 5g of sugar in 20g of water, and the percentage concentration of sugar water solution is (20%).
5÷(5+20)=20%
5. Dissolve (80) grams of alcohol in 20 grams of water, and the concentration of alcohol solution is 80%.
20× 80% ÷1-80% = 80g.
6. A lead-zinc alloy with a weight of 120g, wherein the content ratio of lead and zinc is 2:3. To make lead account for 50% of lead-zinc alloy, it is necessary to melt (24) grams of lead.
Zinc: 120 ÷ (2+3) × 3 = 72g.
Adding lead; 72/50%- 120 = 24g
7. How many grams of pure alcohol and water do you need to add when 40g of alcohol solution A with a concentration of 10% is made into alcohol solution B with a concentration of 100g?
100× 20% = 20g
Alcohol: 20-40× 10% = 16g.
Water: 100-40- 16 = 44g.