(5) 3x-y=14, x-2y=-2, so x=2y-2. Substitute for x in first equation:
3(2y-2)-y=14, 6y-6-y=14, 5y=20, y=4, so x=2y-2=8-2=6.
Solution: x=6, y=4.
(6) Let d=dimes, q=quarters.
d+q=29 (number of coins), 10d+25q=560 (total worth in pennies).
So d=29-q, substitute: 10(29-q)+25q=560, 290-10q+25q=560, 15q=270, q=270/15=18 quarters.
(7) 4 cookies + 1 brownie = $3, 1 brownie = 3 - 4 cookies,
12 cookies + 5 brownies = $11,
12 cookies+5(3-4cookies)=$11,
12 cookies + $15 - 20 cookies = $11,
$4=8 cookies, 1 cookie=4/8=$0.50 or 50¢.
(8) Talk-A-Lot plan T = 21+0.10m
Chat-It-Up plan C = 10+0.15m.
Plans are equal when T=C, 21+0.10m=10+0.15m,
11=0.05m, m=11/0.05=1100/5=220 minutes (costing $43).
