Arianna bought 16 postcards during 4 days of vacation. How many days will Arianna have to spend on vacation before she will have bought a total of 20 postcards? Assume the relationship is directly proportional

5 days

Step-by-step explanation:

16 divided by 4=4 postcards a day

20 divided by 4=5

5 days in total

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a

step-by-step explanation:

let x and 400 - x be the two numbers.  

==> 0.80x + 0.85(400 - x) = 400 - 68 from the statement of the problem.  

< ==> 0.80x + 0.85(400 - x) = 400 - 68  

==> 340 - 0.05x = 332  

< ==> -0.05x = -8 ==> x = 160, the first number ==> 400 - x = 240, the second number.