Find 2 numbers whose sum is 55 and whose product is 684 (show your work)
What are the dimension of a rectangle if it's perimeter is 18.5 and it's area is 21 (show your work)
then A+B = 55 and A*B = 684
Solve for one variable
A = 55-B
Substitute it's value into the other equation so that you only have one variable in the other equation
(55-B)*B = 684
Set equal to zero so that quadratic formula can be used
-B^2 -55B -684 = 0
Use the quadratic formula The Quadratic Formula Explained to solve for B, and then plug that back into either equation to solve for A
We can also see that
A & B divide 684, so they divide 2².3².19 and their product is exactly 2².3².19
All possible couples are :
If a is the first factor, the second has to be 684/a as their product is 684
(1 , 684)
(2 , 2.3².19=342)
(3 , 2².3.19=226)
(4 , ...
Wait, wait ! This is too long to do !!!!
We know that A+B=55. So A & B are inferior to 55 ! Phew ! That reduces a lot the possibilities !
Actually, the only one for which the two factors are inferior to 55 is this one :
(2².3²=36 , 19) -> WOW their sum is 55 !
Did you understand how i got the couples ?