Somewhere
in themathlab.com, locked with a secret password, is a treasure
page. This page has over 10 FREE gifts for you. You are now
looking at the TREASURE FINDER page
that will lead you to this password.

Read
through the page below and do what it says. Write down any parts of the
password as you find them.

You
will need paper and pencil to keep track of your mental math results.

The trick for multiplying by
15 is a combination trick. It involves using the trick
for 10 and the trick
for 5. If you are not skilled at those tricks, go learn how
to use them before you attempt the 15 trick.

Okay, now that you have the
required skills, here we go.

Let's try the problem 24 x
15:

FIRST:

Remember
that 15 can be written as (10 + 5) so 24 is really being multiplied
by BOTH PARTS, 10 & 5.
Think of the problem as two EASY multiplication problems
added together. 24(10 + 5) = (24x10) + (24x5)

SECOND:

Take
24 x 10 and get 240 in your head.

THIRD:

Take
24 x 5 and get 120
(*Remember, once you have 24x10=240, just cut this in half to get 24x5
= 120)

FOURTH:

Now
add 240 and 120 to get 360.

*All four steps can be done
mentally if you like.

Here, you try a few. Click
on the ? to check your answers.
*? answers only work in Internet Explorer.

15 x 8 = ?

30 x 15 = ?

6.2 x 15 = ?

48.6 x 15 = ?

*NOTE:

You can multiply by 1.5 similarly.
Just multiply by 1 and also by 1/2 (which = 0.5), then add the results
together.

EX: 48.6
x 1.5 =

Think:
(48.6 x 1) + (48.6 x 1/2) which gives
+ 48.6
+ 24.3
--------
+ 72.9

*NOTE:

Often in restaurants you
like to leave a 15% tip. This can be easily figured out if you remember
that 10% + 5% = 15%. So find 10% of the bill, then find 5% of the bill,
by cutting the 10% amount in half, then add these results together.

EX: $48.60
x 15% =

Think:
10% of $48.60 is $4.86 (Remember to find 10% of any number
just move the decimal 1 spot to the LEFT.)

Now
half of $4.86 is $2.43. So adding we get,
+$4.86
+$2.43
---------
+$7.29

You try these. Click the ?
to check.

1.5 x 72 = ?

24 x 1.5 = ?

$16.80 x 15% = ?

$6.42 x 15% = ?

Password
Clues

As you
use the 15 tricks to do the following problems IN ORDER, write
down the letter which corresponds to each answer.

When
you KNOW the password

15
x 6 =

15
x 14 =

16
x 15 =

15
x 15 =

30
x 15 =

1.5
x 20 =

90
x 1.5 =

15%
x $1.60 =

$12.50
x 15% =

15
x 2.6 =

1.5
x 13 =

120
x 1.5 =

4.82
x 15 =

$50.62
x 15% =

15%
x $29 =

1.5
x 43 =

15
x 17 =

38
x 1.5 =

15%
x $12.82 =

$15
x 15% =

Now
cross off every a,b,c,and f. You should now be looking
at the correct password.

210
= g

$1.88
= s

225
= a

$4.35
= o

240
= r

450
= a

135
= b

64.5
=c

$1.92
= b

57
= b

$38
= h

255
= u

90
= a

30
= o

39
= b

$0.24
= f

$2.25
= t

180
= f

$7.59
= c

19.5
= s

72.3
= f

$2.50
= r

When
you KNOW the password

To learn even
more of these mental math tricks try the book