In time and work we will learn to calculate and find the time required to complete a piece of work and also find work done in a given period of time. We know the amount of work done by a person varies directly with the time taken by him to complete the work. (i) Suppose A can finish a piece of work in 8 days. Then, work done by A in 1 day = ¹/₈ [by unitary method]. (ii) Suppose that the work done by A in 1 day is ¹/₆ Then, time taken by A to finish the whole work = 6 days. Show
(i) Suppose if a person A can finish a work in n days. Then, work done by A in 1 day = 1/nᵗʰ part of the work. (ii) Suppose that the work done by A in 1 day is \(\frac{1}{n}\) Then, time taken by A to finish the whole work = n days. Problems on Time and Work :1. Aaron alone can finish a piece of work in 12 days and Brandon alone can do it in 15 days. If both of them work at it together, how much time will they take to finish it?Solution: Time taken by Aaron to finish the work = 12 days. Work done by Aaron in 1 day = ¹/₁₂ Time taken by Brandon to finish the work = 15 days. Work done by Brandon in 1 day = ¹/₁₅ Work done by (Aaron + Brandon) in 1 day = ¹/₁₂ + ¹/₁₅ = ⁹/₆₀ = ³/₂₀ Time taken by (Aaron + Brandon) to finish the work = \(\frac{20}{6}\) days, i.e., 6²/₃ days.
2. A and B together can do a piece of work in 15 days, while B alone can finish it 20 days. In how many days can A alone finish the work?Solution: Time taken by (A + B) to finish the work = 15 days. Time taken by B alone to finish the work 20 days. (A + B)’s 1 day’s work = ¹/₁₅ and B’s 1 day’s work = ¹/₂₀ A’s 1 day’s work = {(A + B)’s 1 day’s work} - {B’s 1 day’s work} = (¹/₁₅ - ¹/₂₀) = (4 - 3)/60 = ¹/₆₀ Therefore, A alone can finish the work in 60 days. 3. A can do a piece of work in 25 days and B can finish it in 20 days. They work together for 5 days and then A leaves. In how many days will B finish the remaining work?Solution: Time taken by A to finish the work = 25 days. A’s 1 day’s work = ¹/₂₅ Time taken by B to finish the work = 20 days. B’s 1 day’s work = ¹/₂₀ (A + B)’s 1 day’s work = (¹/₂₅ + ¹/₂₀) = ⁹/₁₀₀ (A + B)’s 5 day’s work (5 × ⁹/₁₀₀) = 4̶5̶/1̶0̶0̶ = ⁹/₂₀ Remaining work (1 - ⁹/₂₀) = ¹¹/₂₀ Now, ¹¹/₂₀ work is done by B in 1 day Therefore, ¹¹/₂₀ work will be done by B in (11/2̶0̶ × 2̶0̶) days = 11 days. Hence, the remaining work is done by B in 11 days. 4. A and B can do a piece of work in 18 days; B and C can do it in 24 days while C and A can finish it in 36 days. If A, B, C works together, in how many days will they finish the work?Solution: Time taken by (A + B) to finish the work = 18 days. (A + B)’s 1 day’s work = ¹/₁₈ Time taken by (B + C) to finish the work = 24 days. (B + C)’s 1 day’s work = ¹/₂₄ Time taken by (C + A) to finish the work = 36 days. (C + A)’s 1 day’s work = ¹/₃₆ Therefore, 2(A + B + C)’s 1 day’s work = (¹/₁₈ + ¹/₂₄ + ¹/₃₆) = (4 + 3 + 2)/72 = \(\frac{9}{72}\) = ¹/₈ ⇒ (A + B + C)’s 1 day’s work = (¹/₂ × ¹/₈) = ¹/₁₆ Therefore, A, B, C together can finish the work in 16 days. 5. A and B can do a piece of work in 12 days; B and C can do it in 15 days while C and A can finish it in 20 days. If A, B, C works together, in how many days will they finish the work? In how many days will each one of them finish it, working alone?Solution: Time taken by (A + B) to finish the work = 12 days. (A + B)’s 1 day’s work = ¹/₁₂ Time taken by (B +C) to finish the work = 15 days. (B + C)’s 1 day’s work = ¹/₁₅ Time taken by (C + A) to finish the work = 20 days. (C + A)’s 1 day’s work = ¹/₂₀ Therefore, 2(A + B + C)’s 1 day’s work = (¹/₁₂ + ¹/₁₅ + ¹/₂₀) = \(\frac{12}{60}\) = ¹/₅ ⇒ (A + B + C)’s 1 day’s work = (¹/₂ × ¹/₅) = ¹/₁₀ Therefore, A, B, C together can finish the work in 10 days. Now, A’s 1 day’s work = {(A + B + C)’s 1 day’s work} - {(B + C)’s 1 day’s work} = (¹/₁₀ - ¹/₁₅) = ¹/₃₀Hence, A alone can finish the work in 30 days. B’s 1 day’s work {(A + B + C)’s 1 day’s work} - {(C + A)’s 1 day’s work}(¹/₁₀ – ¹/₂₀) = ¹/₂₀ Hence, B alone can finish the work in 20 days. C’s 1 days work = {(A + B + C)’s 1 day’s work} - {(A + B)’s 1 day’s work} = (¹/₁₀ – ¹/₁₂) = ¹/₆₀Hence, C alone can finish the work in 60 days. ● Time and Work Time and Work Pipes and Cistern Practice Test on Time and Work ● Time and Work - Worksheets Worksheet on Time and Work 8th Grade Math Practice From Time and Work to HOME PAGE
Didn't find what you were looking for? Or want to know more information about Math Only Math. Use this Google Search to find what you need.
Example 1: If Aarti and Rita can do a job in 8 hours (working together at their respective constant rates) and Aarti can do the job alone in 12 hours. In how many hours can Rita do the job alone? Sol: Let Rita does the work in R days. Using basic work formula the equation would be 1/12 + 1/R = 1/8 ⇒ 8R + 96 = 12R ⇒ 96 = 4R ⇒ 24 = R Working alone, Rita can do the job in 24 hours. Or Example 2: A can do a piece of work in 60 days, which B can do in 40 days. Both started the work but A left 10 days before the completion of the work. The work was finished in how many days? Sol: A left the job 10 days before the completion. So, B worked alone for the last 10 days. First, we will calculate B’s 10 days work, which he did alone. In 10 days B will do 10 × 1/40 = 1/4th of the work. Remaining work 1 - ¼ = ¾ (Which A and B have done together). A and B can do 1/60 + 1/40 work in 1 day. Their one-day’s work is 1/60 + 1/40 = (2 + 3)/120 = 5/120 = 1/24. They can finish the work in 24 days. They would have done three-fourth of the work in 24 × 3/4 = 18 days. ⇒ Total days = 18 + 10 = 28. Or Example 3: A can do a piece of work in 24 days and B in 20 days but with the help of C they finished the work in 8 days. C alone can do the work in how many days? Sol: Using work formula here (1/A) + (1/B) + (1/C) = (1/8) (1/C) = (1/8) - (1/A) - (1/B) ⇒ (1/C) = (1/8) - (1/24) - (1/20) ⇒ (1/C) = (1/30) C can do this work in 30 days. Or
Example 4: If machine X can produce 1,000 bolts in 8 hours and machine Y can produce 1,000 bolts in 24 hours. In how many hours can machines X and Y, working together at these constant rates, produce 1,000 bolts?
Sol: Using formula for work: 1/8 + 1/24 = 1/h ⇒ 4/24 = 1/6. Working together, machines X and Y can produce 1,000 bolts in 6 hours.
Example 5: A and B can do a piece of work in 36 days, B and C in 48 days, A and C can do this work in 72 days. In what time can they do it all working together? Sol: A and B’s one day’s work = 1/36. B and C’s one day’s work = 1/48. C and A’s one day’s work = 1/72. If we add all this it will give us the work of 2A, 2B and 2C in 1 day i.e. (1/36) + (1/48) + (1/72) + (1/16) That also implies that A, B and C’s one day’s work will be half of this i.e. (1/2) x (1/16) = (1/32) From here it can found that they will complete the work in 32 days. Example 6: A can do as much work in 6 days as C in 10 days. B can do as much work in 6 days as C can do in 4 days. What time would B require to do a work if A takes 48 days to finish it? Sol. A : C :: 6 : 10 or (A/C) = (3/5) and B : C :: 6 : 4 or (B/C) = (3/2), (B/A) =(B/C) x (C/A) = (3/2) x (5/3) = (5/2)
Example 7: A can do a piece of work in 48 days and B in 72 days but with the help of C they finished the work in 24 days. Out of the total payment of Rs. 3000, how much should be given to C? Sol: The payment made to anybody is in the proportion of the work done and not in the ratio of days spent. Using work and time formula in 24 days working alone A & B would have done 24/48 = 1/2 and 24/72 = 1/3 of the work. That means they together did 1/2 + 1/3 = 5/6th of the work. Remaining 1/6th of the work must be done by C, the only person present. Now as he did 1/6th of the work, he should be paid 1/6th of the money i.e. 3000 × 1/6 = Rs. 500. In this article we learned, how to solve the time and work questions by applying the basic time and work formula and by using the unit’s approach. Here using the unit’s approach, you make your calculations simple and you can solve the question without writing much. You can make it a point to use this approach in time work problems.
|