Question

Darla needs to purchase nine more stamps than envelops. Each stamp cost $0.10, and each envelope costs $0.13 . If she pays $2.51, how many stamps and envelops does she buy.

Answer 1

This is a systems of equations.

s = stamp, e = envelope

`\left \{ {{e + 9 = s} \atop {.1s+.13e=2.51}} \right.`

Substitute e + 9 for s.

.1(e + 9) + .13e = 2.51

Simplify.

.1e + .9 + .13e = 2.51

Simplify.

.14e + .9 = 2.51

Subtract .9 from both sides.

.14e = 1.61

Divide both sides by .14.

e = 11.5

Now, you can input e into the other equation.

11.5 + 9 = s

Simplify.

20.5 = s

s = 20.5, e = 11.5