pls solve these

It takes Ali 30 minutes to mark a paper. Aslam only needs 25 minutes to mark a paper. If they both start marking papers at 100 AM, at what time they will finish marking at the same time?

Two bus tickets from Rawalpindi to Islamabad and three tickets from
Rawalpindi to Murree cost Rs.770 but three tickets from Rawalpindi to
Islamabad and two tickets from Rawalpindi to Murree cost Rs.730. What are
the fares for cities Islamabad and Murree from Rawalpindi?

A school has enough provision of food for 52 days. After 20 days a group of
400 students arrives and the food would have last for 24 days only. How many students are there in the school actually?

A man walks 2km towards North. Then he turns to East and walks 10km. After this he turns to North and walks 3km. Again he turns towards East and walks 2km. How far is he from the starting point?

Ali and Aslam:
This is basically LCM — least common multiple.

So Ali will mark at
10
10.30
11
11.30

Aslam will mark at
10
10.25
10.50
11.15

Question is asking: where do multiples of 30 and 25 minutes coincide?

Answer is

2 | 30, 25
3 | 15, 25
5 | 5, 25
5 | 1, 5
| 1, 1

2 x 3 x 5 x 5 = 150 minutes

So 10 AM + 150 minutes is 12.30 PM.

——————————————

Bus tickets:

Let RI be Rawalpindi–Islamabad
RM be Rawalpindi–Murree

We are told that
2RI + 3RM = 770 ———— 1
3RI + 2RM = 730 ———— 2

We have to find RI and RM. Solve the simultaneous equations.

Rearrange equation 1:
RI = (770 - 3RM)/2

Insert into equation 2:

(3/2)*(770 - 3RM) + 2RM = 730
2310 - 9RM + 4RM = 1460
- 5RM = -850
RM = 170

So Rawalpindi-Murree is Rs. 170.
Which means since 770 - 3(170) = 2RI
then RI = Rs. 130

And sure enough, this is correct because
3x170 + 2x130 = 770

——————————————

School:

School has food for x students, lasting 52 days
20 days past, so food left is for 32 days
But now 400 new students arrive, and this falls from 32 to 24 days

x students meant 32 days
x+400 meant 24 days

Amount of food is equal in both, so just equate them:
32 * x = 24 * (x+400)
Solve for x, which comes out to 1200 students (originally).

——————————————

Man walking:

Just make a diagram on the exam paper.

2 km North (up), then 10 km East (right), then 3 km North (up) then 2 km East (right), so

Total distance UP = 2 + 3 = 5 km
Total distance RIGHT = 10 + 2 = 12 km

Hypotenuse of a triangle which has sides 12 and 5 km long is 13 km.

Are we betting on the same paper structure as last year with 4 questions in Section I or something similar to 2016?

thank you so much!

[QUOTE=Engr Jahanzeb;911576]The anwser is amplitude. Frequency only changes the pitch of a sound, e.g a girl's voice can be as loud as a guy's, but their pitch is different(Bhari awaz vs patli awaz).

Great job...

Q1. Write short notes on any TWO of the following: (5 each)
a) Communication Satellite:
A communications satellite is an artificial satellite that relays and amplifies radio telecommunications signals through a transponder. It basically creates a communication channel between a source transmitter and a receiver at different locations on earth. Communications satellites use a wide range of radio and microwave frequencies
b) Geothermal energy:
Geothermal energy, form of energy conversion in which heat energy from within Earth is captured and harnessed for cooking, bathing, space heating, electrical power generation, and other uses.
Process of heat formation:
The temperature of the earth is high due to molten rocks and larva which reaches to the water and generate steam. Thus, the steam is used for the genera
Pros and cons of geothermal energy:
• Renewable resource: Geothermal energy is free and abundant. The constant flow of heat from the Earth makes this resource inexhaustible and limitless to an estimates time span of 4 billion years.
• Green energy: Geothermal energy is non-polluting and environment-friendly as no harmful gases are evolved with the use of geothermal energy unlike the use of fossil fuels. Also, no residue or by-product is generated.
• Generation of employment: Geothermal power plants are highly sophisticated and involve large scale research before installation. This generates employment for skilled and unskilled labors at a very large scale at each stage of production and management.
• Can be used directly: In cold countries, the geothermal energy is used directly for melting of ice on the roads, heating houses in winters, greenhouses, public baths etc. Although the initial cost of installation is very high, the cost for maintenance and repair is negligible.
• Transportation and transmission: Unlike fossil fuels, geothermal energy cannot be transported easily. Once the tapped energy is harnessed it can only be used efficiently in the nearby areas. Also, with the transmission, there are chances of emission of toxic gases getting released into the atmosphere.
• High installation cost: The installation of geothermal power plants to get steam from deep under the Earth requires a huge investment in terms of material and human resource.
• Intensive research required: Before setting up a plant, extensive research is required, as the sites can run out of steam over a period of time due to a drop in the temperature as a result of excessive or irregular supply of inlet water.
• Limited to particular regions: The source of geothermal energy is available in limited regions, some of which are highly inaccessible such as high rise mountains and rocky terrains, which renders the process economically infeasible in many of the cases.
• Impact to the environment: Geothermal sites are present deep under the earth, so the process of drilling may result in the release of highly toxic gases into the environment near these sites, which sometimes prove fatal to the workforce involved in the process.

Water pollution:
Water pollution is the contamination of water bodies like oceans, seas, lakes, rivers, aquifers, and groundwater usually caused due to human activities. Water pollution is any change in the physical, chemical or biological properties of water that will have a detrimental consequence of any living organism. Basically, water pollution is the release of substances into surface. In addition to the release of substances, such as chemicals or microorganisms, water pollution may also include the release of energy, in the form of radioactivity or heat, into bodies of water.
Sources of Water Pollution
Some of the most commonly occurring water pollutants are:
a. Domestic Waste
b. Industrial effluents
c. Insecticides and pesticides
d. Detergents and Fertilizers
e. Urbanization
f. Deforestation
Effects of Pollution of Water
Some affects of water pollutions are given below:
a. Diseases
b. Destruction of ecosystem
c. Growth of algae
d. Effects the food chain
Way forward to get rid of water pollution:
The best way to prevent large-scale water pollution is to try and reduce its harmful effects. There are various small changes one can make to protect oneself from a scary future where water is scarce.
a. Save Water
b. Better treatment of sewage
c. Use environmentally friendly products
d. Reduce the use of herbicides, pesticides, and fertilizers
e. Proper sewage treatment and management
f. Avoid direct dumping into water systems
g. Skip the use of plastics

Communications satellite

A communications satellite is a type of artificial satellite that is placed in Earth’s orbit for the purpose of sending and receiving communication data between a source and destination. It is used to provide data communication and relaying services for televisions, radio, telecommunication, weather and Internet services.

A communications satellite is a wireless communication device in Earth’s orbit that uses a transponder to send and receive data from Earth. It is primarily used to redirect communication data from one Earth-based communication station to another station. Typically, a communications satellite works when it receives data from terrestrial stations in the form of electromagnetic waves. The data is usually sent via large satellite dishes. Based on the intended destination, the communications satellite redirects the waves to the corresponding station.

Communications satellites are vital for remote areas that do not have access to traditional landlines for telephone or Internet services.

What is hydropower?

Hydropower is, by far, the most used form of renewable energy resource in the world. It’s also the oldest method of power generation. Statistically, the world’s electricity produced by hydropower stands at 21%, and the total number of people supplied by energy generated from hydropower plants is a staggering 1,250,000,000. A record 25 countries rely on hydropower for 90% of their electricity. All these statistics point to the fact that hydropower will still rule the world although other renewable forms of energy like solar and wind are fast gathering steam.
Hydropower is simply the process of harnessing the kinetic energy from moving water to produce power. Hydropower is classified as a renewable energy due to the fact that the water cycle is continually renewed by the sun. Hydropower was first used in mechanical millings like grinding grain. In the modern world, hydropower plants utilize turbines and generators to produce electricity.

Various Advantages of Hydropower

1. Cheap source of energy
Although the upfront costs of constructing and installing a hydropower plant are high, once it’s functional, the costs relating to operation and maintenance become extremely low.

2. It’s a renewable resource
With hydropower production, water is not used up. The hydropower technologies only derive the energy of moving water and convert it into electricity.

3. Eco-friendly
Hydroelectric power is a clean source of energy, which means it contributes small amounts of greenhouse gasses to the atmosphere.

4. Hydropower is flexible
Hydropower has a vital benefit of being able to be accumulated. This means that it can be directed to meet variation in demand.

5. Boosts the electric grid
When blackout occurs, or when demand is at peak, hydropower can flawlessly be fed into the main electrical grid compared to other sources of energy.

6. Economical Advantage
When hydropower is introduced to remote areas that lacked the resource, it promotes commerce, industry, and assists build up infrastructure and upgrade existing ones such as roads and navigation.

7. Increases awareness of the area
Setting up a hydropower plant increases awareness of the areas nearby. Focus turns to animal species and ecosystems of the surrounding areas.

8. Picks up water shortage slack
Water is naturally used to power businesses and homes. Nonetheless, in the course of converting moving water into energy, rainwater is harvested and utilized for irrigation and drinking.