When Master Li processes a batch of parts, two fifths of the work is finished. According to this calculation, how many hours does it take Master Li to complete all the tasks?

When Master Li processes a batch of parts, two fifths of the work is finished. According to this calculation, how many hours does it take Master Li to complete all the tasks?

Set the workload to 1
Efficiency = two thirds / two fifths = 5 / 3
1÷5/3＝3/5

Master Li has finished two fifths of the whole batch of parts. If he processes another 80 parts, he will just finish half of the whole,
How many parts does Master Li process?

80 parts: 1 / 2-2 / 5 = 1 / 10
This batch of parts: 80 △ 1 / 10 = 800 (pieces)
Master Li processes parts: 800 × 2 / 5 = 320 (pieces)

Processing a batch of parts, processing 60 parts per hour, five hours later, there are just two fifths of the total number of parts left. How many parts are there in this batch?
Why does that count?
Please tell me the tips
The solution equation cannot be used

500

Master Wang processes a batch of parts. He processes 60 parts per hour. After three hours, two fifths of the total parts are left. How many parts are there in this batch
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This problem can be solved by equation and formula. Equation: suppose there are x parts in total, then the equation can be listed: 60 × 3 = X-2 | 5xc. Simplify, get: 180 = 3 | 5x. Multiply both sides of the equation by 5 at the same time, get: 900 = 3x. Coefficient into one, get: 300 = X. answer: there are 300 parts in total. Formula: 60 × 3 | (1-2 | 5) = 180 | 3 | 5 =