Question 156349
Let t = number of three cent stamps, e = number of eight cent stamps, and f = number of fifteen cent stamps.

Since the number of 8 cent stamps is one less than triple the number of 3 cent stamps, we can write this equation:
e = 3t - 1

Since the number of 15 cent stamps is six less than the number of 8 cent stamps, we can write this equaation:
f = e - 6

Let's substitute 3t-1 for e:

f = 3t-1-6
f =3t-7

We can write an equation showing the total value of the stamps like this:

.03t + .08e + .15f = 2.47

Now, since we have e and f in terms of t, let's substitute those expressions in the total equation:

.03t + .08(3t-1) + .15(3t-7) = 2.47

Expanding we get:

.03t + .24t - .08 + .45t - 1.05 = 2.47

Combining like terms we now have:

(.03 + .24 + .45)t - 1.13 = 2.47

.72t - 1.13 = 2.47

Adding 1.13 to both sides, we now have:
.72t = 3.60

Dividing both sides by .72, we get:
.72t/.72 = 3.6/.72
t = 5

Putting t into the first equation we had, we get:
e = 3(5) - 1, so e = 14
and putting 14 for e in the second equations, we get:
f = 14 - 6, so  f = 8

Finally, we have 5 three cent stamps, 14 eight cent stamps, and 8 fifteen cent stamps.

Checking the result:
5(.03) + 14(.08) + 8(.15) = 2.47
.15 + 1.12 + 1.20 = 2.47
2.47 = 2.47