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Q:

If the mean of a, b, c is M and ab + bc + ca = 0, then the mean of $\frac{a^{2} + b^{2} + c^{2}}{3}$ is :

A) M	B) 3 M^2
C) 2 (M/3)	D) M^2

Answer & Explanation Answer: B) 3 M^2

Explanation:

We have : ( a + b + c) / 3 = M or (a + b + c) = 3M.

Now. ${(a + b + c)}^{2} = {(3 M)}^{2} = 9 M^{2}$ .

$< = > a^{2} + b^{2} + c^{2} + 2 (a b + b c + c a) = 9 M^{2}$

$a^{2} + b^{2} + c^{2} = 9 M^{2}, (a b + b c + c a = 0)$

Required mean = $(\frac{a^{2} + b^{2} + c^{2}}{3}) = \frac{9 M^{2}}{3} = 3 M^{2}$ .

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Q:

The average price of three items of furniture is Rs. 15000. If their prices are in the ratio 3:5:7, the price of the cheapest item is :

A) 6000	B) 7000
C) 8888	D) 9000

Answer & Explanation Answer: D) 9000

Explanation:

Let their prices be 3x, 5x and 7x.

Then, 3x + 5x + 7x = (15000 * 3) or x = 3000.

Cost of cheapest item = 3x = Rs. 9000.

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Q:

1.Water boils at 100 degree C

2.Water freezes at 0 degree C

Conclusion: At low pressure ,water boils at lower temperature

The conclusion drawn is

A) True	B) false
C) either probably true or probably false	D) Irrelavent

Answer & Explanation Answer: D) Irrelavent

Explanation:

It is irrelavent

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Q:

The average temperature of the town in the first four days of a month was 58 degrees. The average for the second, third, fourth and fifth days was 60 degrees. If the temperatures of the first and fifth days were in the ratio 7 : 8, then what is the temperature on the fifth day ?

A) 62 degrees	B) 64 degrees
C) 65 degrees	D) 66 degrees

Answer & Explanation Answer: B) 64 degrees

Explanation:

Sum of temperatures on 1st, 2nd, 3rd and 4th days = (58 * 4) = 232 degrees ... (1)

Sum of temperatures on 2nd, 3rd, 4th and 5th days - (60 * 4) = 240 degrees ....(2)

Subtracting (1) From (2), we get :

Temp, on 5th day - Temp on 1st day = 8 degrees.

Let the temperatures on 1st and 5th days be 7x and 8x degrees respectively.

Then, 8x - 7x = 8 or x = 8.

Temperature on the 5th day = 8x = 64 degrees.

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Q:

1.Oxygen is a gas

2.This cylinder contains gas

Conclusion: This cylinder contains Oxygen

The conclusion drawn is

A) True	B) Probably true
C) False	D) Irrelavent

Answer & Explanation Answer: A) True

Explanation:

It is true

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Q:

The average of 11 numbers is 10.9. If the average of the first six numbers is 10.5 and that of the last six numbers is 11.4, then the middle number is :

A) 10.5	B) 11.5
C) 12.5	D) 13.5

Answer & Explanation Answer: B) 11.5

Explanation:

Middle numbers = [(10.5 x 6 + 11.4 x 6) - 10.9 x 11] = (131.4 - 119-9) = 11.5.

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Q:

The average age of the boys in a class is 16 years and that of the girls is 15 years. The average age for the whole class is :

A) 15	B) 20
C) 21	D) data inadequate

Answer & Explanation Answer: D) data inadequate

Explanation:

Clearly, to find the average, we ought to know the number of boys, girls or students in the class, neither of which has been given.

So, the data provided is inadequate.

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Q:

The average of the two-digit numbers, which remain the same when the dibits inter-change their positions, is :

A) 53	B) 54
C) 55	D) 56

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