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81. If the numerator of a fraction is increased by 14 and the denominator is decreased byy 13, the new fraction obtained is 3364. What was the original fraction ?

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Solution:
Let the fraction be xy
Then,
x+14y13=33643(4x+1)4(3y1)=33644x+13y1=3364×434x+13y1=111616(4x+1)=11(3y1)64x+16=33y1164x33y=27
Which cannot be solved to find xy
Hence, the original fraction cannot be determined from the given data.
82. If doubling a number and adding 20 to the result gives the same answer as multiplying the number by 8 and taking away 4 from the product, the number is :

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Solution:
Let the number be x
Then,
⇔ 2x + 20 = 8x - 4
⇔ 6x = 24
⇔ x = 4
83. Out of six consecutive natural numbers if the sum of first three is 27, what is the sum of the other three ?

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Solution:
Let the six numbers be, x , (x + 1), (x + 2), (x + 3), (x + 4) and (x + 5)
Then,
⇔ x + (x + 1) + (x + 2) = 27
⇔ 3x + 3 = 27
Required sum :
= (x + 3) + (x + 4) + (x + 5)
= 3x + 12
= (3x + 3) + 9
= 27 + 9
= 36
84. The difference between a two-digit number and the number obtained by interchanging the two digits is 63. Which is the smaller of the two numbers ?

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Solution:
Let the ten's digit be x and unit's digit be y
Then,
(10x+y)(10y+x)=639(xy)=63xy=7
85. If the numerator of a fraction is increased by 200% and the denominator is increased by 300%, the resultant fraction is 1526. What was the original fraction ?

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Solution:
Let the fraction be xy
Then,
x+200% of xy+300% of y=15263x4y=1526xy=1526×43xy=1013
86. If 50 is subtracted from two-third of number, the result is equal to sum of 40 and one-fourth of that number. What is the number ?

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Solution:
Let the number be x
Then,
23x50=14x+4023x14x=905x12=90x=(90×125)x=216
87. The sum of two numbers is 25 and their difference is 13. Find their product :

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Solution:
Let the numbers be x and y
Then,
x + y = 25 and x - y = 13
4xy=(x+y)2(xy)24xy=(25)2(13)24xy=6251694xy=456xy=114
88. The sum of seven consecutive numbers is 175. What is the difference between twice the largest number and thrice the smallest number ?

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Solution:
Let the seven numbers be x, (x + 1), (x + 2), (x + 3), (x + 4), (x + 5) and (x + 6)
Then,
⇔ x + (x + 1) + (x + 2) + (x + 3) + (x + 4) + (x + 5) + (x + 6) = 175
⇔ 7x + 21 = 175
⇔ 7x = 154
⇔ x = 22
Required difference :
= 2(x + 6) - 3x
= 12 - x
= 12 - 22
= -10
89. The number obtained by interchanging the two digits of a two-digit number is lesser than the original number by 54. If the sum of the two digit of the number is 12, then what is the original number ?

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Solution:
Let ten's digit = x
Then, unit's digit = (12 - x)
[10x+(12x)]    [10(12x)+x]   =54
18x108=5418x=162x=9
So, ten's digit = 9 and unit's digit = 3
Hence, original number = 93
90. A fraction is such that if the double of the numerator and the triple pf the denominator is changed by +10 percent and -30 percent respectively, then we get 11 percent of 1621. Find the fraction :

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Solution:
Let the fraction be xy
Then,
110% of 2x70% of 3y=11% of 162122x21y=11100×1621xy=(11100×1621×2122)xy=225