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Case study (4 Marks)

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Question 14 Marks
A hotel has 320 rooms and 32 cleaners to maintain them. With full capacity of staff, it took 2 h to clean all the rooms.
(i) On Monday 20% of the cleaners were not available. Will the cleaning of all rooms takes more time? How can you say so?
(ii) Ishan says, "The number of cleaners available in the hotel is directly proportional to the time taken by them to clean the rooms."
Mira says, "The number of clearners available in the hotel is inversely proportional to the time taken by them to clean the rooms."
Who is correct? Given reason.
(iii) Equal number of rooms are allocated for each staff member for cleaning. How many rooms each cleaner had to maintain?
(iv) The hotel administration hired 8 more cleaners. What is the change in number of rooms maintained by each cleaner?
(a) The total number of room increases by 2
(b) The total number of room decreases by 2
(c) The total number of room increases by 3
(d) The total number of room decreases by 3
Answer
(i) Yes, because with $20 \%$ less staff, work has to be performed by available staff impacting the total time.
(ii) Mira is correct.
Because the more number of staff available in the hotel for cleaning, less time will be required to finish it which means the number of room cleaning staff available in the hotel is inversely porportional to the time taken by them to clean the rooms.
(iii) Since, to clean 320 rooms, the required cleaners are 32.
$\therefore$ Number of rooms each cleaners had to maintain
$
=\frac{320}{32}=10 rooms
$
(iv) (b) The hotel administration hired 8 more cleaners.
$\therefore$ Number of cleaners $=32+8=40$
and number of rooms $=320$
$\therefore$ Each cleaner will maintain the number of rooms
$
=\frac{320}{40}=8
$
Previously, they had to maintain 10 rooms.
$\therefore$ Change in number of rooms maintained by each cleaner $=10-8=2$
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Question 24 Marks
Deepak and his family went on a road trip by car. They visited four cities. City 1 was 500 km from their home. The petrol tank in their car has a capacity of 35 litres. The car runs 20 km on one litre.
City 1City 2City 3City 4
Distance travelled by the car500100015002000
From City 4, they travelled 500 km to reach home.
(i) How many litres of petrol did they use to complete the road trip?
(a) 100 $\qquad$ (b) 125 $\qquad$ (c) 200 $\qquad$ (d) 2500
(ii) The family travelled 500 km In a day. What is the smallest number of days in which the road trip can be completed?
(iii) The car travelled at a uniform speed of $75 km / h$ between City 3 and City 4 . How much distance did car travel in 20 min ?
(iv) The family started their journey from City 3 at 10 am . By what time will they reach half the distance to City 4 ?
(a) 12 pm $\qquad$ (b) 1:30 pm $\qquad$ (c) 1:20 pm $\qquad$ (d) 3 pm
Answer
(i) (b) The distance between cities $=500 km$
Given that the car runs 20 km on one litre.
$\therefore$ Petrol it will take on running $1 km=\frac{1}{20}$
$\therefore$ To travel 500 km the petrol, it will take
$
=\frac{1}{20} \times 500=25 \text { litres }
$
Since, they visited 4 cities and then travelled 500 km more to reach home.
Therefore, the petrol used to complete the trip
$
\begin{array}{l}
=(25 \times 4)+25 \\
=100+25 \\
=125 \text { litres }
\end{array}
$
(ii) The family travelled 500 km in a day i.e. the distance to reach each city. There are 4 cities ( 500 km each) and they travelled 500 km more to reach home.
$\therefore$ The road trip will take 5 days.
(iii) The car travelled at a uniform speed of $75 km / hr$ between City 3 and City 4.
i.e. in 60 minutes car travels $=75 km$
In 1 min car will travel $=\frac{75}{60}$
$\therefore$ In 20 min car will travel $=\frac{75}{60} \times 20=25 km$
(iv) (c) The family started their journey from City 3 at 10 am.
We know that car is travelling with speed of $75 km / h$. i.e. to cover 75 km the time it takes $=1 h$
To cover 1 km , the time it takes $=\frac{1}{75}$
$\therefore$ To cover 250 km , the time it takes $=\frac{250}{75}=\frac{10}{3} h$
$
\begin{array}{l}
=3.33 h \\
\approx 3.3 h
\end{array}
$
Therefore, they will reach half the distance by $1: 20 pm$ if they start their journey at 10 am .
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Case study (4 Marks) - MATHS STD 8 Questions - Vidyadip