Rate Of Work By D.fisher

Rate Of Work By D.fisher - Transcript

by D Fisher

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Marge can clean the house in 3 hrs Lisa can clean it in 5 hrs How long will it take them to clean the house if they both work together

Marge can clean the house in 3 hrs so she does 3 of the house per hour
1

Lisa can clean the house in 5 hrs so she does 5 of the house per hour
1

Let T be the time in hours 1 3

T

1 5

T 1

1 1

3T 5T 1
1

1

15 3T 5T 15 1 5T 3T 15 8T 15 T 8 7 1 8 hrs
15

Bart can wash the car in 20 min Homer can wash it in 30 min How long will it take them to wash the car if they both work together

Bart can wash the car in 20 min so he does 1 20 of the car per min

Homer can wash the car in 30 min so he does 30 of the car per min
1

Let M be the time in minutes 1 20

M

1M 30

1

1 1

20M 30M 1
1

1

60 20M 30M 60 1 3M 2M 60 5M 60 M 12 min

Mr Skinner can enroll 15 students per hr Mr Chalmer can enroll 20 students per hr How long will it take them to enroll 140 students working together

Minutes work better than hours Mr Skinner enrolls 15 students per 60 min so he enrolls 15 60 or 1 4 students per min

Minutes work better than hours Mr Chalmer enrolls 20 students per 60 min so he enrolls 20 60 or 1 3 students per min

1 1

4M 3M 140
1

1

12 4M 3M 12 140 3M 4M 1680 7M 1680 M 240 min 4 hrs

Mrs Krabappel can grade a set of 1 papers in 1 2 hrs Miss Hoover can grade them in 80 min How long will it take them to grade one set if they both work together

Minutes work better than hours Mrs Krabappel grades 90 of a set per min
1

Miss Hoover grades 1 80 of a set per min

1 1

90M 80M 1
1

1

720 90M 80M 720 1 8M 9M 720 17M 720 6 M 42 17 min

Approximately how long would it take them to grade 3 sets if they both work together

1 1

90M 80M 3
1

1

720 90M 80M 720 3 8M 9M 2160 17M 2160 1 M 127 17 min A little more than 2 hrs