Linear Equation
- If the sum of one-half and one-fifth of the number exceeds one-third of that number by 7 1/3 , the number is
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Let us assume the number is a.
Given that 7 1/3 = 22/3
According to question,
a x 1/2 + a x 1/5 = a x 1/3 + 22/3
Solve the equation.Correct Option: C
Let us assume the number is a.
Given that 7 1/3 = 22/3
According to question,
a x 1/2 + a x 1/5 = a x 1/3 + 22/3
⇒ a/2 + a/5 = a/3 + 22/3
⇒ a/2 + a/5 - a/3 = 22/3
⇒ (15a + 6a - 10a)/30 = 22/3
⇒ (15a + 6a - 10a) = 30 x 22/3
⇒ 11a = 10 x 22
⇒ a = 10 x 2
⇒ a = 20
- If 24 is subtracted from a number, it reduces to its four-seventh. what is the sum of the digits of that number ?
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Let us assume the number is n.
According to question,
If 24 is subtracted, it becomes 4/7 of the number.
⇒ n - 24 = n x 4/7
Solve the equation.Correct Option: C
Let us assume the number is n.
According to question,
If 24 is subtracted, it becomes 4/7 of the number.
n - 24 = n x 4/7
⇒ n - 4n/7 = 24
⇒ (7n - 4n)/7 = 24
⇒ 3n/7 = 24
⇒ 3n = 24 x 7
⇒ n = 24 x 7/3
⇒ n = 8 x 7
⇒ n = 56
Sum of the digits of the number = 5 + 6 = 11
- The Sum of all terms of the arithmetic progression having 10th terms except for the 1st term, is 99, and except for the 6th term , 89. Find the 3rd terms of the progression if the sum of the 1st and the 5th term is equal to 10.
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Let us assume the first term is a and common difference is d.
Formula for nth term of Arithmetic Progression = a + ( n - 1 ) x d
According to question,
Sum of the first term and the fifth term = 10
t1 + t5 = 10
Formula of sum of n terms for Arithmetic Progression,
Sn = n/2[ 2a + ( n - 1 ) x d ]
Again According to question,
The sum of all terms of the Arithmetic Progression, except for the 1st term = 99
S10 - first term = 99
Solve the equation.Correct Option: B
Let us assume the first term is a and common difference is d.
Formula for nth term of Arithmetic Progression = a + ( n - 1 ) x d
So first term t1 = a + ( n - 1 ) x d
t1 = a + (1 - 1) x d = a + 0 x d = a
Fifth term t5 = a + ( n - 1 ) x d = a + (5 - 1) x d = a + 4d
According to question,
Sum of the first term and the fifth term = 10
t1 + t5 = 10
⇒ a + a + 4d = 10
⇒ 2a + 4d = 10
⇒ a + 2d = 5.............................(1)
Formula of sum of n terms for Arithmetic Progression,
Sn = n/2[ 2a + ( n - 1 ) x d ]
Put the value of n = 10, Since total number of terms is 10 .
⇒ S10 = 10/2[ 2a + ( 10 - 1 ) x d ]
⇒ S10 = 5[ 2a + 9 x d ] = 10a + 45d
Again According to question,
The sum of all terms of the Arithmetic Progression, except for the 1st term = 99
S10 - first term = 99
⇒ 10a + 45d - a = 99
⇒ 9a +45d = 99
⇒ a + 5d = 11.................................(2)
Subtracts Equation (1) from Equation (2), we will get,
⇒ a + 5d - a - 2d = 11 - 5
⇒ 3d = 6
⇒ d = 2
Put the value of d in equation (1), we will get
⇒ a + 2 x 2 = 5
⇒ a + 4 = 5
⇒ a = 5 - 4
⇒ a = 1
Since tn = a + ( n - 1) x d
find the third term by putting the value of a , n and d. we will get,
t3 = 1 + ( 3 - 1) x 2 = 1 + 2 x 2 = 1 + 4 = 5
So 3rd term of Arithmetic Progression is 5.
- If the mth term of an Arithmetic Progression (AP) is 1/n and nth term is 1/m, then find the sum of mn terms.
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let us assume a be the first term and d the common difference.
According to Question,
mth term of an Arithmetic Progression (AP) is 1/n
Use the Arithmetic Progression formula for mth term,
⇒ a + ( m - 1 ) x d = tm
Use the Arithmetic Progression formula for nth term,
⇒ a + ( n - 1 ) x d = tn
Now according to question,
Sum of mn terms = mn/2(2a + ( mn - 1) x d)
Smn = mn/2(2a + ( mn - 1) x d)
Solve the equationCorrect Option: C
let us assume a be the first term and d the common difference.
According to Question,
mth term of an Arithmetic Progression (AP) is 1/n
Use the Arithmetic Progression formula for mth term,
⇒ a + ( m - 1 ) x d = tm
⇒ a + ( m - 1 ) x d = 1/n
⇒ a + md - d = 1/n .......................(1)
Use the Arithmetic Progression formula for nth term,
⇒ a + ( n - 1 ) x d = tn
⇒ a + ( n - 1 ) x d = 1/m
⇒ a + nd - d = 1/m.........................(2)
Subtracts Equation (1) from Equation (2) , we will get
⇒ a + nd - d - (a + md - d) = 1/m - 1/n
⇒ a + nd - d - (a + md - d) = 1/m - 1/n
⇒ a + nd - d - a - md + d = 1/m - 1/n
⇒ nd - md = 1/m - 1/n
⇒ d(n - m) = 1/m - 1/n
⇒ d(n - m) = (n - m)/mn
⇒ d = 1/mn.......................................(3)
Put the value of d in Equation (1), we will get,
⇒ a + md - d = 1/n
⇒ a + ( m x 1/mn ) - 1/mn = 1/n
⇒ a + 1/n - 1/mn = 1/n
⇒ a = 1/n - 1/n + 1/mn
⇒ a = 1/mn.....................................(4)
Now according to question,
Sum of mn terms = mn/2(2a + ( mn - 1) x d)
Smn = mn/2(2a + ( mn - 1) x d)
Put the value of a and d in above equation, we will get,
Smn = mn/2 [ 2 x 1/mn + ( mn - 1) x 1/mn ]
Smn = mn/2 [2/mn + 1 - 1/mn ]
Smn = mn/2 [ 1 + 1/mn ]
Smn = mn/2 [ ( mn + 1 )/mn ]
Smn = mn/2 (1 + mn)/mn
Smn = 1/2 (1 + mn)
Smn = (1 + mn)/2 = (mn + 1)/2
- what is the sum of all the two-digits numbers which when divided by 7 gives a remainder of 3 ?
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According to question,
First Two Digit Number, which is divided by 7 and give the remainder 3, will be 10.
Last Two Digit Number, which is divided by 7 and give the remainder 3, will be 94.
The common difference between two consecutive numbers will be 7.
This series will be like →10, 17, 21 ,............................ 94.
Here First Number a = 10, Last number tn = 94, Common Difference d = 7 ;
Using the Formula for Last Number tn = a + (n - 1) x d;
⇒ a + (n - 1) x d = tn
Using the formula for the sum of Arithmetic Progression.
Sn = n/2 [ First Number + Last Number ] ;
Put the value of n , First Number and Last Number.
Solve the equation.Correct Option: B
According to question,
First Two Digit Number, which is divided by 7 and give the remainder 3, will be 10.
Last Two Digit Number, which is divided by 7 and give the remainder 3, will be 94.
The common difference between two consecutive numbers will be 7.
This series will be like →10, 17, 21 ,............................ 94.
Here First Number a = 10, Last number tn = 94, Common Difference d = 7 ;
Using the Formula for Last Number tn = a + (n - 1) x d;
⇒ a + (n - 1) x d = tn
Put the value of a , d and tn in above equation.
⇒ 10 + (n - 1) x 7 = 94
⇒ 10 + 7n - 7 = 94
⇒ 7n + 3 = 94
⇒ 7n = 94 - 3 = 91
⇒ n = 91/7
⇒ n = 13
Using the formula for the sum of Arithmetic Progression.
Sn = n/2 [ First Number + Last Number ] ;
Put the value of n , First Number and Last Number, we will get,
Sn = 13/2 [ 10 + 94 ]
Sn = 104 x 13/2
Sn = 52 x 13
Sn = 676