Linear Equation


  1. 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


  1. 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



  1. 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.


  1. 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 equation

    Correct 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



  1. 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