The sum of two numbers is 56 and the difference is 20 . what are the numbers

x + y is 56 or  

x+y=56

the difference means you subtract them..  

so  

x-y = 22

you have two equations and two unknowns, you can use elimination or substitution

x+y=56  

x-y = 22

add the 2 equations together...  

x+y=56  

x-y = 22

and I get:  

2x = 78 divide both side by 2

x = 78/2 = 39  

substitute this back into the original equations (anyone of them) to find what y is equal to.  

x+y=56  

39 + y = 56  

y = 56-39 = 17  

so you get : x =39, y = 17

check your answers by substituting

x+y=56 39+17 = 56 check  

x-y = 22 39 -17 = 22 check

step-by-step explanation: a reaction is first order. if the initial reactant concentration is 0.0200 m, and 25.0 days later the concentration is 6.25 x 10-4 m, then its half-life is:

25% is the answer