Question

5. The temperature at 12 noon was 10°C above zero. If it decreases at the rate
of 20°C per hour until midnight, at what time would the temperature be
8°C below zero? What would be the temperature at mid-night?
6. In a class test (+3) marks are given for every correct answer and (-2)
marks given for every incorrect answer and no marks for not attempting
any question. (i) Suraiya scored 20 marks. If she has got 12 correct
answers, how many questions has she attempted incorrectly? (ii) Raziya
scores - 5 marks in this test, though she has got 7 correct answers. How
many questions has she attempted incorrectly?
7. An elevator descends into a mine shaft at the rate of 6 m/min. If the
descent starts from 10 m above the ground level, how long will it take to
reach - 350 m.
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Answer 1

Answer:

1. At 12 noon, the temperature =10°C above zero

The temperature is decreasing at 2°C per hour

8°C below zero =−8°C

So, total fall in temperature from 10°C to 0°C and from 0°C to −8°C=18°C

Since the temperature falls 2°C in every one hour.

Therefore, to decrease 18°C, time taken = 18/2

= 9 hours

Present time is 12 noon so, the time when the temperature is −8°C

=12noon+9hours

So, The time at which the temperature will be −8°C=9PM

At 9 PM, the temperature is −8°C, the temperature at 12 midnight will be =

(−8°C)+(−2°C×3hours)

=(−8°C)+(−6°C)

=−14°C

2.Radhika scored 12×3=36 marks. as 3 marks are for correct answer

final score of radhika is 20.

she got 16 marks negative. as −2 marks are for incorrect answer

therefore she made 2/16

=8 incorrect answer.

2) Mohini scored 7×3=21 marks. as 3 marks are for correct answer

final score of radhika is −5.

she got 26 marks negative. as −2 marks are for incorrect answer

therefore she made

2/26

=13 incorrect answer.

3.Distance descended is denoted by a negative integer,

Initial height =+10 m

Final Depth =−350 m

Total distance to be descended by the elevator =(−350)−(+10)=−360 m

Given, the time is taken by the elevator to descend −6 m=1 minute

Thus, time taken by the elevator to descend −360 m=

(−6)/(−360)

[from the formula : speed=

time

distance]

=60 minutes

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