Darlene bought some 30 cent and some 60 cent candy bars. Altogether she bought 10 candy bars and paid a total of $4.20. How many candy bars at each price did she buy?

Question

anonymous · Answer

help!

anonymous · Answer

t stands for 30 cent candy bars
s stands for 60 cent candy bars 

t + s = 10 ---> t = 10 - s
.30t + .60s = 4.20

now sub 10 - s in for t in the 2nd equation
.30t + .60s = 4.20
.30(10 - s) + .60s = 4.20
3 - .30s + .60s = 4.20
3 + .30s = 4.20
.30s = 4.20 - 3
.30s = 1.20
.30s/.30 = 1.20/.30
s = 4

now sub 4 in for s in the first equation...
t + s = 10
t + 4 = 10
t = 10 - 4
t = 6

check...
.30t + .60s = 4.20
.30(6) + .60(4) = 4.20
1.80 + 2.40 = 4.20
4.20 = 4.20 (correct)

ANSWER : Darlene bought 6 thirty cent candy bars at 1.80 and she bought 4 sixty cent candy bars at 2.40 for a total of 10 candy bars costing 4.20

Do you understand how I got this answer ?