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DSQ

by golu23 » Sun Jan 15, 2012 5:17 am
1)In the xy plane,at what 2 points does the graph of y(x+a)(x+b) intersect the X axis?
A+B=-1
The graph intersects Y axis AT (0,-6)

2)What is the Avg of 11 conecutive integers
The avg of first nine integers is 7
The avg of last nine integers is 9

Guys i have no idea how to solve these problems.
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by rijul007 » Sun Jan 15, 2012 5:41 am
golu23 wrote: 2)What is the Avg of 11 conecutive integers
The avg of first nine integers is 7
The avg of last nine integers is 9
The avg of first nine integers is 7
For 9 consecutive integers, 5th integer should be the integer
3,4,5,6,7,8,9,10,11

These are the first 9 integer, so the 11 consec int would be
3,4,5,6,7,8,9,10,11,12,13
Average = 8


The avg of last nine integers is 9
Similarly last 9 integers would be
5,6,7,8,9,10,11,12,13

The 11 integers would be
3,4,5,6,7,8,9,10,11,12,13
Average = 8


Option D
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by mj78ind » Sun Jan 15, 2012 5:41 am
golu23 wrote:1)In the xy plane,at what 2 points does the graph of y(x+a)(x+b) intersect the X axis?
A+B=-1
The graph intersects Y axis AT (0,-6)

2)What is the Avg of 11 conecutive integers
The avg of first nine integers is 7
The avg of last nine integers is 9

Guys i have no idea how to solve these problems.
Problem 1: can be rephrased as
y = (x+a)(x+b)
= x^2 +(a+b)x + ab

Stmt 1: a+b = -1. INSUFFICIENT as ab could be anything, thus changing the roots and hence the points where the graph meets the x axis.

Stmt 2: ab = -6, again a+b could be anything. Hence roots will change. Hence INSUFFICIENT.

Stmt 1 + Stmt 2: gives us a+b and ab thus now there will be unique roots for the equation. SUFFICIENT. Hence C

Problem 2:
Stmt 1: we know the sum of n numbers in an arithmetic progression is S = (n/2)(2a + (n-1)d), where n = number of terms, a = first term, d = difference between two consecutive terms.
From stmt 1, we know n = 9, S = 7*9, d = 1, hence a can be found hence Sum of 11 terms can be found. SUFFICIENT.
Stmt 2 - we see that again n, d and S are given hence Sum of 11 terms can be found. SUFFICIENT.

Hence D
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by golu23 » Sat Jan 21, 2012 6:08 am
1)A certain list consists of several integers. Is the product of integers in the list positive?
A)THE PRODUCT OF THE GREATEST AND THE SMALLEST IS POSITIVE
B)THERE IS AN EVEN NO OF INTEGERS IN THE LIST

2)Jane walked for 4 miles What was her avg speed for 2 miles?
a)HER AVG PEEED FOR 4 MILES WAS 3.2 KMPH
b)IT TOOK JANE 15 MINS LONGER TO WALK THE SECOND 2 MILES THAN FIRST 2 MILE

In problem 2 i know that first statement is not sufficient but i don't know how to use the second statement.
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