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71. If x : 7.5 = 7 : 17.5, then the value of x is -

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Solution:
=x:7.5=7:17.517.5x=7.5×7x=7.5×717.5=3
72. The value of x where x : 213 :: 21 : 50 is -

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Solution:
=x:213::21:5050x=73×2150x=49x=4950
73. If 2 : (1+3)  :: 6 : x, then x is equal to -

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Solution:
=2:(1+3)::6:x2x=6(1+3)x=6(1+3)2=3(1+3)=3+3
74. In an alloy, the ratio of copper and zinc is 5 : 2. If 1.250 kg of zinc is mixed in 17 kg 500 gm of alloy, then the ratio of copper and zinc will be = ?

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Solution:
The ratio of copper and zinc is 5 : 2
i.e 5x : 2x
Quantity of initial mixture = 17.5 kg
∴ 5x + 2x = 352
⇒ x = 52
Quantity of Copper in initial mixture
=52×5=252kg
Quantity of Zinc in initial mixture
=52×2=5kg
Now after adding 1.250 kg of zinc
= 5 + 1.250
= 6.250 kg
= 254kg
∴ New Ratio of copper : zinc
=252:254=2:1
75. The income of A, B and C are in the ratio 7 : 9 : 12 and their spending are in the ratio 8 : 9 : 15. If A saves 14 th of his income then the savings of A, B and C are in the ratio of = ?

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Solution:
Let income of A, B and C are 7x, 9x and 12x respectively
and expenditure of A, B and C are 8y, 9y and 15y respectively
Incomeof,A×14=SavingofA(given)7x8y=7x×1428x32y=7x21x=32yx:y=32:21
∴ The ratio of savings of A, B and C
⇒ (7x - 8y) : (9x - 9y) : (12x - 15y)
⇒ (7 × 32 - 8 × 21) : (9 × 32 - 9 × 21) : (12 × 32 - 15 × 21)
⇒ (224 - 168) : (288 - 189) : (384 - 315)
⇒ 56 : 99 : 69
76. What will be the simplest form of the ratio 3 hours : 1 day?

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Solution:
1 day = 24 hours.
∴ Given ration = 3 : 24
= 1 : 8
77. In a proportion the product of 1st and 4th terms is 40 and that of 2nd and 3rd terms is 2.5x. Then the value of x is.

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Solution:
Product of 1st and 4th terms (extremes) = product of 2nd and 3rd terms (means)
2.5x=40x=402.5=16
78. If 20% of A = 30% of B = 16 of C, then A : B : C is -

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Solution:
20%of A=30%of B=16of C20A100=30B100=C6A5=3B10=C6=k(say)A=5K,B=10k3,C=6kA:B:C=5k:10k3:6k=5:103:6=15:10:18
79. Two numbers are in the ratio 17 : 45, One - third of the smaller is less than 15 of the bigger by 15. The smaller number is = ?

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Solution:
A:B17:4517x:45xGiven17x×13+15=45x×1517x+453=9x17x+45=27x10x=45x=4510Smaller number is =4510×17=76510=7612
80. 25% of A's income is equal to 35% of B's income. The ratio of the incomes of A and B is -

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Solution:
=25% of A=35% of B25100A=35100BA4=7B20AB=720×4=75A:B=7:5