B. the number problem should master the representation of decimals in the number problem. C. Basic formula of engineering problems: workload = working hours × working efficiency. D. the problem of sailing against the current V =v still water +v water. V current =v still water -v water.
Tree planting problem
1 The problem of planting trees on unclosed lines can be divided into the following three situations:
Number of plants = number of segments = total length/plant spacing = plant spacing × plant number = total length/plant number
Total length = plant spacing × number of plants = total length ÷ number of plants
The question of profit and loss
(Profit+Loss) ÷ Difference between two distributions = number of shares participating in distribution.
(Big profit-small profit) ÷ Difference between two distributions = number of shares participating in distribution.
(big loss-small loss) ÷ The difference between two distributions = the number of shares participating in the distribution.
encounter a problem
Meeting distance = speed × meeting time
Meeting time = meeting distance ÷ speed and the sum of speed = meeting distance ÷ meeting time 17 Tracing the problem.
Catch-up distance = speed difference × catch-up time = catch-up distance ÷ speed difference = catch-up distance ÷ catch-up time 18 flow problem
Downstream velocity = still water velocity+countercurrent velocity = still water velocity-current velocity = (downstream velocity+countercurrent velocity) ÷2
Water velocity = (downstream velocity-countercurrent velocity) ÷2
Concentration problem
Solute weight+solvent weight = solution weight.
The weight of solute/solution × 100%= concentration.
Solution weight × concentration = solute weight/solute concentration = solution weight.
Profit and discount problem
Profit = selling price-cost
Profit rate = profit/cost × 100%= (selling price/cost-1)× 100% fluctuation amount = principal × fluctuation percentage discount = actual selling price/original selling price × 100% (discount
Interest = principal × interest rate× time
After-tax interest = principal × interest rate × time ×( 1-20%)