Math for Grownups (22 page)

The picture must be 9 inches tall.

What if you set up the proportion with the widths as the numerators and the heights as the denominators?

How about that—the same answer. Math
is
flexible!

Before pulling out the sewing machine or setting up the table saw, ask yourself, “Does it make more sense to buy what I’m about to make?”

You may want the experience of building something from scratch. But you also may need to keep a little change in your pocket. It’s always a good idea to consider what your craft will cost the family budget.

Rita loves Halloween, and she loves making her kids’ costumes. This year, her 10-year-old daughter has requested a velvet-like cape and gown so that she can dress as some obscure character from her favorite novel about magical kids.

The pattern Rita is using calls for 7 yards of fabric, 2 fancy fasteners, and 3 yards of fringe. Looking at the Sunday circular for the local fabric store, she sees that crushed panne velvet is on sale for $2.99 per yard and the fringe is priced at $4 per yard. Rita guesses that the fasteners are about $5 each. To estimate her costs, she adds everything together:

(7 • $2.99)
+
(3 • $4)
+
(2 • $5)

(In case you lost track, that’s 7 yards of fabric at $2.99 per yard, 3 yards of fringe at $4 per yard, and 2 frog clasps at $5 each.)

$20.93
+
$12
+
$10
=
$42.93

A terrifying price!

Rita is starting to think that a trip to a thrift shop might be a better investment of her time and money. Sometimes doing it yourself just isn’t worth it.

On math worksheets from school, you have exactly the information you need. In real life, though, you have to decide which numbers are relevant—and how. That’s not always as simple as it sounds.

Tad wants to build a birdhouse out of scrap wood. He’s interested in attracting chickadees, so he does some research, and this is what he learns:

Base of the interior: 4" by 4"

Height of the interior: 10"

Distance of entrance from the floor: 8"

Diameter of entrance: 11/8;"

Height above ground: 6' to 15'

Which of the pieces of information on this list will he use to build the birdhouse?

Basically, Tad will be constructing a box with a big hole drilled into it. To figure out how much wood he’ll need, he uses the dimensions of the box: 4" by 4" by 10". Those dimensions tell him the dimensions of each side.

each of 4 sides: 4" by 10"

top and base: 4" by 4"

Tad will need to cut four pieces of wood that measure 4" by 10" and two pieces that measure 4" by 4". (Any box has six sides.)

The next two measurements in his list tell Tad where and how large to drill the entrance to the birdhouse.

But that last bit of information? It’s not relevant. It is only
after
he’s built the birdhouse that Tad needs to know how high to install it.

At the Bank: Income Minus Expenses Equals Happiness (or Misery)

Old-timers remember the good old days when they paid their bills with a check and trusted the local bank to give good interest rates and honest loans. They had a pension and Social Security, so they didn’t play the stock market or invest in a 401(k) plan.

Those times are long gone.

These days, virtually everyone invests in Wall Street. Pensions—and maybe even Social Security—will soon appear only in history books. Credit and debit cards have replaced cash. And checkbooks? What are those?

Managing finances is probably the most math-intensive part of modern daily life. And a lot hangs on those calculations: your retirement, your kids’ college tuition, your salary.

Unlike gardening or finding the sale price on a big-screen TV, this stuff can make you or break you. It literally pays to have a good handle on financial math.

Dad harped about a lot of things. Have you studied for your test? Did you take out the trash? Are you changing the oil in your car? Did you call your mother? Have you drawn up a budget?

But that last question is one of those times when he was absolutely right. You oughta have a budget. Yep, they’re a pain you know where, but budgets can keep you on track financially.

It’s New Year’s Day, and Darrel is pondering his resolutions over a bowl of black-eyed peas. For sure, he wants to reach level 65 in
Purple Heart: World at War
. And he wants to ask out that cute girl in the apartment next door.

But Darrel is also sick and tired of worrying about money. He’s got a good job as a computer programmer, but for some reason, he’s still ending up with too many bills at the end of the month. Last year, he had to sell his first-edition
Spiderman
comic to pick up a little extra cash. He knows he needs to add a really, really boring New Year’s resolution to his list: keeping a personal finances budget.

He vaguely remembers what his high school consumer math teacher told him about budgets. At least he remembers that there are three parts: income, regular expenses, and occasional expenses. His income should be greater than all of his expenses put together.

He writes the name of the month at the top of the page, March, and then adds his current monthly income: $2,655.

He’s careful to put in his take-home income, not his before-tax income, because that’s all he can spend.

Now he brainstorms all of his regular expenses, including his weekly comic store purchases. Some of his expenses, such as his electric bill, vary a bit from month to month, but he adds up the last year’s worth and divides by 12 to get a monthly average.

So far, so good. It looks like Darrel is living within his means, but what will happen when he adds in his occasional expenses? He brainstorms again, consulting his online banking records for guidance.

He divides that total by 12 to get his average monthly expense: $601.67.

If you’re wondering whether you’re spending too much of your income on certain line items in your budget, check out this advice from budgeting gurus.

• Groceries should account for about 18% of your monthly gross income.
  
• Housing should cost no more than 28% to 33% of your monthly gross income.
  
• You should be saving at least 10% to 20% of your monthly gross income.
  

Speaking of savings, you should have at least 4 months of your monthly take-home income in the bank—in an account that you can get to easily. This amount serves as an emergency fund, for when the pipes burst or, worse, you find yourself on the unemployment line.

He adds his regular and occasional expenses together: $2,648 + 601.67 = $3,249.67. That’s more than his monthly take-home pay! He’s going to have cut back. It takes Darrel only a few moments to recalibrate his budget. He’s going to reduce the number of comic book conventions he goes to, and he’s going to cut down his satellite television expenses. He notices that he can put some money each month into his languishing savings account. And if, at the end of the year, he gets that raise he’s been expecting, he can put even more away for a rainy day.

This little bit of math gives Darrel a boost of confidence—enough confidence that he picks up the phone and calls his cute neighbor.

One way to balance out your budget is to increase your income. But is a higher salary always the best—or most reasonable—option? Negotiating your salary package, which includes vacation time, benefits, and perhaps even commissions, is all part of the equation.

Congratulations! You just landed a brand-new job as human resources director for Darling Day Care Centers.

But before you settle into the work of managing teachers, assistants, and lunch preparation staff for this 40-center company, you need to negotiate your pay. (And you thought the job interview was tough!)

They’ve offered you a $48,000 salary, which is not bad. Still, you’re hoping they can go up to $50,000.

If they can’t, you have an idea. An extra two weeks of vacation could be a pretty good deal. But how does giving you two more weeks of vacation compare to upping their offer by $2,000?

To find out, you need to know the monetary value of two extra vacation weeks. And that number depends on your hourly rate.

Being on salary means you’ll be paid for holidays or any vacation taken. So even though you won’t be working 40 hours a week, 52 weeks a year, you’re paid for that time. For the entire year, you’ll be compensated for working

40 • 52
=
2,080 hours

Now you can find your hourly wage with simple division:

$48,000
/
2,080
=
$23.08

So how much would the company be paying you to lounge on a tropical beach? Multiply your hourly rate by the number of working hours in two weeks (or 80 hours).

$23.08 • 80
=
$1,846.40

Huh. The cost of an extra two weeks of vacation is pretty darned close to the extra $2,000 you’d like to see in your salary. You can live with that.

It’s time to negotiate.

Glenda may be the Good Witch, but she’s not so good with her money. She really, really, really wanted that Bubble Transportation Vehicle (BTV). What better way to impress the Munchkins
and
make it from her apartment to Munchkinland in 30 seconds flat?

But the darned thing cost a lot of money. Money that she didn’t have. Always the optimist, she simply pulled out her Bank of Oz gold card and said, “Swipe it!”

Now good Glenda is in trouble. The interest rate on her card is 18%, and she’s worried that she’ll never pay off the debt.