If y = x^2 + c is the equation of a curve, does this curve

Question

1. If y = x^2 + c is the equation of a curve, does this curve lie completely above the x-axis

a) c > 0
b) (1, 4) is a point on the curve

2. If the average of five different positve numbers is 18, and if the largest number is 40, then the median of the five numbers could be one of the following

I 5
II 15
III 25


3. Select 2 teachers out of 9 eg. 3 eng, 4 math and 2 hist - what is the prob that both are eng teachers

4. If t, t/4 and t/8 are all positive integers between 1 and 1000 inclusive, how many values could be there for t 
(250, 200, 199, 50, 51)

rthothad · Answer

1. A - y has to be positive for the curve to lie above the x-axis
2. II & III
3. 3/18 * 2/17 = 1/51
4. I get (1000/8 = 125) but I don't see that in your answer choice, so I think I am unable to follow the question

damit · Answer

Hi could you please explain problem number 1. 

on #2 according to me, 5 could be the mean also. Since ave is 18 sum of the 5 numbers is 18*5 = 90
THe numbers could be 40, 38, 5, 4, 3 which all add up to 90

3 is correct

on #4 you have to consider that t/8 and t/4 fall between 1 - 1000. So for example if t started at 8 and went to 8008 then we would go outside of 1000. so you half this number for t/4 (which would end at 4004) and then half again for t sp 500/2 = 250 is my answer.

rthothad · Answer

1. If you need to mark a point below the x-axis, the point will have to have a negative value for y-axis, it may be something like (2, -5), 'A' says y is always positive, so the curve has to lie above the x-axis
2. Yes you are correct, I made a mistake.
4. According to my understanding of the question is that it asking for all values of t that would be divisible by 4 & 8, only 125 values will be divisbile by both 4 & 8.

Folaa3 · Answer

For the first question, i got A same reasoning as rthothad.

second question, i think the median could be any of 15 or 25. There are no constraints in the question except that the number are different thus it could be either 15 or 25

Third question , i got 1/12 (3/9 * 2/8) (what am i doing wrong :oops:

)

fourth i got 125 as t must definitely be a multiple of 4 and 8 and whatever is a multiple of 8 is a multiple of 4 and there are 125 multiples of 8 between 1 and 1000 inclusive.

) fourth i got 125 as t must definitely be a multiple of 4 and 8 and whatever is a multiple of 8 is a multiple of 4 and there are 125 multiples of 8 between 1 and 1000 inclusive.

gotoknow3 · Answer

Q2: Answer should be I and II only.

sum of the remaining 4 numbers should be 50, so 25 cannot be the median since the numbers are +ve and different.

july05 · Answer

hey, rthothad, could you please explain how you got 1/51 in #3? i agree with Folaa that it should be 3/9*2/8=1/12

rthothad · Answer

I think you did not read the question properly, the question is a bit misleading with the 'Select 2 teachers out of 9 eg.', where 'eg.' is also a department so there are a total of 18 teachers

HowManyToGo · Answer

1) D , y can never be negative using either , hence always above x axis
2) I & II 
-25 cannot happen as then the 4th number should be greater than 25, in which case the first two numbers should be negative.
3) 9c2/18c2 ?
4)1000 although there is no such option.(8,16,24,32,....800.......8000)

HMTG.

qpoo · Answer

- A

- I,II

Total is: 90, take away 40, the other 4 number add up to 50
If one of the four is 25, the other 3 will add up to 25.
That means neither of them will be greater than 25.
So, of the 5 numbers, biggest is 40, second biggest 25, third ...
25 thus cannot be the median

- Teacher question is confusing. I wonder what 'eg.' is, other than
'for example' :wink:

- 125[/list]

- 125

sparky · Answer

1. D. 2) defines c, so we know the equation of the curve
2. I and II only

5 might work
5-x1 + 5-x2 + 5 + 5+x3 + 40 = 5*18 =90 => x3-x1-x2 = 30 
15 should work
x3-x1-x2 = -10
25 doesn't work
x3-x1-x2 = -50 

3. 1/3* 1/4 = 1/12

Folaa3 · Answer

What is the official answer for question 3? I need to know just so i have to re-revise my probability

HIMALAYA · Answer

you can do this prob question # 3 in two ways.
i) the prob of getting 2 eng (using prob method) = (3/9)(2/8)=1/12
ii) the prob of getting 2 eng (using combination) = (3c2)/9c2=3/36= 1/12

Arsene_Wenger · Answer

1. Missed it, but agree on (A)
2. I and II
3. 1/12
4. 125.

If y = x^2 + c is the equation of a curve, does this curve

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