## Note on Simultaneous Linear Equation in Two Variables

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### Solving Simultaneous Linear Equations

Let us consider a problem related to our daily life,
The total cost of 2 kg of tea and 3 kg of coffee is Rs. 725. If 3 kg of tea and 2 kg of coffee are bought, the cost becomes Rs. 75 less. What is the per kg price of each?

Here,

\begin{align*} i.\: \text{Combined cost of 2kg tea and 3 kg coffee} &= Rs. 725 \\ ii. \: \text{Total cost of 3 kg tea and 2 kg coffee} &= Rs. 725 - Rs. 75 \\ &= Rs. 650 \\ \end{align*}

Here are two prices which should be found.
Let the cost of 1 kg of tea = Rs. x
& the cost of 1 kg of coffee = Rs. y
Then, 2x + 3y = 725 ........... (i)
3x + 2y = 650 ...........(ii)

There are two variables x and y in the above pair of equations. The given pair of linear equations represents a pair of straight lines while plotting on the graph. The method of obtaining the value of the two variables (order pairs) which satisfy both the equation is known as 'solution of equations'. If the pair of values of two variables involved in a pair of equations satisfies both the equations, those equations are called linear simultaneous equation.

• Simultaneous equations are broadly used to find two unknown quantities.
• By solving the equations we can find the unknown quantities.
• In the application of simultaneous equations, the coefficient of x is the same in both equations.
• We subtract one equation from other to eliminate x.
• We can make a pair of simultaneous equations under the two given conditions.
.

### Very Short Questions

Let, the cost of the book = Rs x, the cost of the pen = Rs y

From 1st condition , x + y = 475 --------------(i)

From 2nd condition , x - y = 75 --------------(ii)

(x + y) + (x - y) = 475 + 75

or, 2x = 550

or x = $$\frac {550}{2}$$

∴ x = 275

Then, Putting the value of x in equation (i)

x + y = 475

or, 275 + y = 475

or, y = 475 - 275

∴ y = 200

∴ Cost of book = Rs 275 and cost of pen = Rs 200

$$Let, the age of father = x years, the age of son = y years From 1st condition , x + y = 32 --------------(i) From 2nd condition , x - y = 24 --------------(ii) Adding (i) and (ii), (x + y) + (x - y) = 32 + 24 or, 2x = 56 or x = \( \frac {56}{2}$$

∴ x = 28

Then, Putting the value of x in equation (i)

x + y = 32

or, 28 + y = 32

or, y = 32 - 28

∴ y = 4

∴ Age of father = 28 years and age of son = 4 years

\)

Let, thetwo numbers are x and y.

From 1st condition , x + y = 80--------------(i)

From 2nd condition , x - y = 40--------------(ii)

(x + y) + (x - y) =80 + 40

or, 2x =120

or x = $$\frac {120}{2}$$

∴ x =60

Then, Putting the value of x in equation (i)

x + y =80

or, 60+ y = 80

or, y =80 - 60

∴ y =20

∴ The required numbers are 60 and 40.

$$Let, thetwo numbers are xand y. From 1st condition , x+ y = 45o--------------(i) From 2nd condition ,x- y = 15o--------------(ii) Adding (i) and (ii), (x + y) + (x - y) =45o+15o or, 2x =60o or x = \( \frac {60^o}{2}$$

∴ x =30o

Then, Putting the value of x in equation (i)

x + y = 45o

or, 30o+ y =45o

or, y = 15o

∴ y =15o

∴ The required anglesare 45o and 15o.

\)

$$Let, thetwo numbers are x and y. From 1st condition , x =3y--------------(i) From 2nd condition , x +y = 32--------------(ii) Putting value of x in(ii), 3y + y=32 or, 4y=32 or y= \( \frac {32}{4}$$

∴ x =8

Then, Putting the value of yin equation (i)

x = 3y

or, x = 3× 8

or, y = 24

∴ y =20

∴ The required numbers are 8 and 24.

\)

Let the two numbers be x and y and x be the greater one .

From 1st condition, x + y = 14 ---------(i)

From 2nd condition, x= y + 4 ------------(ii)

Putting value of x in equation (i)

x + y = 14

or, y + 4 + y = 14

or, 2y = 14 - 4

or, 2y = 10

or y = $$\frac {10}{2}$$

∴y = 5

Now, putting value of y in equation (ii)

x = y + 4 = 5 + 4 = 9

Hence, the required numbers are 9 and 5.

Let, the number be x.

According to question,

x2 - 10 = 54

or, x2 = 54 + 10

or,x2 = 64

or,x2 = (±8)2

∴ x = ±8

Let, breadth of the pond (b) = x m

Then, length of the pond = (x + 10) m

Perimeter of the pond (P) = 120m

or, 2 (l + b) = 120

or, l + b = $$\frac{120}{2}$$

or, l + b = 60

or, ( x + 10) + x = 60

or, 2x + 10 = 60

or, 2x = 60 - 10

or, 2x = 50

or, x = $$\frac{50}{2}$$

or, x = 25

and Length = (x +10) = 35 m

Hence, the length and the breadth of the pond are 35m and 25m respectively.

0%

2, 3
2, -1
3, 1
1, 2

2,3
1, 3
4, 3
3,4

22, 36
26, 33
34, 30
25, 30
• ### The total cost of TV and Radio is Rs 500. If the watch is cheaper than Radio by 150, find their cost.

Rs 125, Rs 375
Rs 120, Rs 300
Rs 150. Rs 350
Rs 175, Rs 325

3, 2
2, 1
3, 1
2, 3

35, 12 years
36, 11 years
30, 10 years
31, 11 years
• ### Ramesh is three times as old as his son. If the differences of their ages is 24 years. Find their present ages.

36 years, 12 years
37 years, 8 yeras
30 years, 5 years
35 years, 10 years

45, 32
40, 30
42, 30
55, 35

5, 2
6, 3
4, 2
2, 1

6, 18
4, 11
5, 12
7, 15
• ## You scored /10

Forum Time Replies Report
##### Rijen

In two digit number, the product of two digit is 14 and if 45 are sutracted from the numbers, the number will be reversed what is the number find it

##### Aasesh

If the age of father was 13 times than his son 1 year ago.Now the age of father is equal to cube of his son age.Find their present age.