Video Transcript
John saved up 45 dollars, and he
plans to use his savings to download music and movies. Each song costs one dollar and 15
cents and each movie costs two dollars and 55 cents. If John downloads three songs and
one movie each week, determine the number of dollars, 𝑑, he will have after 𝑚
weeks?
Each song costs one dollar and 15
cents to download. And we know that John downloads
three songs each week. This means that the amount of money
John spends on songs each week is one dollar 15 cents multiplied by three. This is equal to three dollars and
45 cents as one dollar multiplied by three is three dollars and 15 cents multiplied
by three is 45 cents.
Each movie costs two dollars and 55
cents to download. And John downloads one of these
each week. This means that he spends two
dollars and 55 cents per week downloading movies as two dollars and 55 multiplied by
one is still two dollars and 55 cents.
We can, therefore, calculate the
total amount that John spends on downloads per week by adding three dollars and 45
cents to two dollars and 55 cents. This is equal to six dollars as 45
cents plus 55 cents is one dollar and three dollars plus two dollars is equal to
five dollars. Five plus one equals six.
We could set this out as a column
addition calculation, if required. Five plus five is equal to 10. We put a zero in the hundredths
column and carry the one. Four plus five is equal to
nine. Adding the one we carried gives us
10. We put a zero in the tenths column
and once again carry a one. Three plus two equals five. Adding the one we carried gives a
six. We must remember to keep the
decimal point in the same place. Therefore, three dollars and 45
cents plus two dollars 55 cents is equal to six dollars exactly.
We were asked to calculate the
number of dollars 𝑑 that John has after 𝑚 weeks. He started with 45 dollars. And we’ve worked out that he spends
six dollars per week on downloads. This means that 𝑑, the number of
dollars, is equal to 45 minus six 𝑚. We need to multiply the six dollars
by 𝑚, the number of weeks.
If John downloads three songs and
one movie each week at one dollar 15 cents and two dollars 55 cents, respectively,
if he starts with 45 dollars, then the number of dollars he will have after 𝑚 weeks
is 45 minus six 𝑚.
