Question 197531
Write an equation or a system of equations that can be used to solve each
 of the following problems. In each case, state what the variable or
 variables represent.(solution of the equations is not required.)
:
a) Julie can keypunch a certain number of computer cards in 4 hours.
 It takes Pat 6 hours to keypunch the same number of computer cards.
 If Julie and pat work together, how long will it take them to keypunch that number of cards?
;
Let t = no. of hrs required when working together
Let the completed job = 1
{{{t/4}}} + {{{t/6}}} = 1
:
:
b) The sum of the digits of a two-digit number is 7. If the digits are
 reversed, the new number is two more than twice the original number.
 Find the original number.
:
Two digits; x and y: The number = 10x + y
"sum of the digits of a two-digit number is 7."
x + y = 7
y = (7-x); use for substitution
:
"If the digits are reversed, the new number is two more than twice the original number.
10y + x = 2(10x + y) + 2
10y + x = 20x + 2y + 2
10y - 2y = 20x - x + 2
8y = 19x + 2