math problem of the day

[jas_fluidm]

L= {-6, -5, -4, -3, -2}
P = {-2, -1, 0, 1, 2, 3}

If an integer is to be randomly selected from set L above and an integer is to be randomly selected from set P above, what is the probability that the product of the two integers will be negative?

A. 0
B. 1/3
C. 2/5
D. 1/2
E. 3/5

[jas_fluidm]

no. of possible values to be negative/all possible values from the sets
=5*3/5*6
=1/2

[jas_fluidm]

in order to get negative integer either m should be negative and n positive
probability of L is negative =5/5=1
probability of P is positive 3/6=1/2
probability of m negative and m positive is 1*1/2=1/2

[jas_fluidm]

The sum of the even numbers between 1 and k is 79*80, where k is an odd number, then k=?

[jas_fluidm]

answer is 159

[jas_fluidm]

A certain right circular cylinder has a radius of 5 inches. There is a kind of liquid filled in this cylinder to the height of 9 inches. If this liquid is poured completely into a second right cylinder, then the liquid will fill the second cylinder to the height of 4 inches. What is the radius of the second cylinder, in inches?

[jas_fluidm]

Answer will be as follows:

Volume of 1st cylinder=2*pi*5^2*9
Volume of 2nd cylinder=2*pi*r^2*4
so, 5^2*9=r^2*4
=> r=Sq rt(25*9/4)=7.5

[mohin]

The sum of the even numbers between 1 and k is 79*80, where k is an odd number, then k=?

Answer is 159. How? please help........................

[Khandoker Samaher Salem]

Nice post.