0

# Emily has some five-dollar bills and some ten-dollar bills. She has 15 bills, and she has 120 dollars. How many five-dollar bills does she have?

You have to yse a table chart

### 3 Answers by Expert Tutors

Philip P. | Effective and Affordable Math TutorEffective and Affordable Math Tutor
5.0 5.0 (443 lesson ratings) (443)
1
Let F = The number of \$5 bills and T = the number of \$10 bills.  She has 15 bills total, so:

F+T = 15
T = 15-F

She has \$120 total:

\$120 = (\$5)*F + (\$10)*T
\$120 = \$5*F + (\$10)*(15-F)         [Substitute 15-F in place of T]
120 = 5F + 150 - 10F
-30 = -5F

6 = F

Check:
T= 15-F = 15=6 = 9

\$120 = (\$5)*6 + (\$10)*9
\$120 = \$30 + \$90
\$120 = \$120
Check!
Yohan C. | Math Tutor (up to Calculus) (not Statistics and Finite)Math Tutor (up to Calculus) (not Statist...
4.0 4.0 (1 lesson ratings) (1)
0
Hi Malaiyah,

Here is how to do it:

(\$10) x + (\$5) y = \$120

x + y = 15

x    y
10   5

15   0
14   1
13   2
12   3
11   4
10   5
9    6   !
8    7
7    8
6    9
5    10

First, it has to add up to 15 bills and number of \$5 bills must be even because it has to end with 0.  If there are 2 \$5 bills, it will add up to \$140.  If there are 4 \$5 bills, it will add up to \$130.  And if there are 6 \$5 bills, it will make up \$120: \$10 x 9 which is \$90 and \$5 x 6 which is \$30.  As you add them together, you will get \$120.  There you have it.

Good luck.

Tip of the day:  Multiples of 5s will only end with 5 or 0.  5 times any odd number will always end with 5 and 5 times any even number will always end with 0.
Francisco P. | Rigorous Physics TutorRigorous Physics Tutor
5.0 5.0 (228 lesson ratings) (228)
0
x = \$5 dollar bills

y = \$10 dollar bills

x + y = 15

5x + 10y = 120

Solve for y from the first equation and substitute into the second to get

5x + 10(15-x) = 120

5x + 150 - 10x = 120

-5x = -30

x = 6, so y = 9

There are six \$5 bills and nine \$10 bills.