Compound interest is the starting amount x (1+ the interest rate as a decimal)^ the time in years=the final amount.
In your case, the equation will be $1000*(1+0.10)^how many years= the final amount.
You made 3/20 of the 400 cards, which is 60 cards.
Let the speed for the first 12 mi be x mi/h, the speed for 18 mi was (x+4) mi/h
thus given that
time=distance/speed
the average time will be:
3=(12+18)/(x+x+4)
3=30/(2x+4)
solving for x we get
3(2x+4)=30
6x+6=30
6x=24
x=4 mi/hr
Answer: 12 mi/hr
5x + 2(x + 1) ≤ 23
Distribute the 2.
5x + 2x + 2 ≤ 23
Combine like terms.
7x + 2 ≤ 23
Subtract 2 from both sides.
7x ≤ 21
Divide both sides by 7
x ≤ 3