Answer:
Mark has 12 quarters
Step-by-step explanation:
I did all of it, nickles, dimes, and of course, quarters..
So, Let +n+ = the number of nickels he has
Let +d+ = the number of dimes he has
Let +q+ = the number of quarters he has
given:
(1) +q+=+2n+
(2) +d+=+n+%2B+3+
(3) +5n+%2B+10d+%2B+25q+=+420+
( the units for this equation is cents , for instance,
$4.20 is 420 cents
All you have to do is substitute (1) and (2) into (3)
so that the only variable is +n+, then solve
(3) +5n+%2B+10%2A%28+n+%2B+3+%29+%2B+25%2A%282n%29+=+420+
(3) +5n+%2B+10n+%2B+30+%2B+50n+=+420+
(3) +65n+%2B+30+=+420+
Subtract +30+ from both sides
(3) +65n+=+390+
(3) +n+=+6+
And since
(2) +d+=+n+%2B+3+
(2) +d+=+6+%2B+3+
(2) +d+=+9+
Also, since
(1) +q+=+2n+
(1) +q+=+2%2A6+
(1) +q+=+12+
: Mark has 6 nickels, 9 dimes, and 12 quarters
