Five students received the same text message at 9.00
Each of them sent the message to 5 more students al
10:00 AM. Each of those students sent the message to
5 more students at 11:00 AM

a is 8.b is 10.c is 10.5. d is -.5

step-by-step explanation:

just minus the smallest number from the biggest.

x= cost per bracelet

number of bracelets * x + shipping charge = total cost

so

9x+9=72

ending amount = beginning amount / (2^n)

where "n" = number of half-lives (or elapsed time / half-life)

ending amount = 50 mg / (2 ^10 / 5.3)

ending amount = 50 mg / (2 ^ 1.8867924528)

ending amount = 50 m / 3.6981210597

ending amount = 13.5203794557 mg

or about 13.5 mg remain

source: