Use your iPhone to impress your friends with these cool calculator tricks
The iPhone calculator is great for crunching numbers in a pinch, but you can also use it to have some fun with your friends and family. Here are some cool calculator tricks you can use to find someone's phone number, guess their age and astound them with your math wizardry. If you have any tricks up your own sleeve, please share them in the comments.
Can I Get Your Phone Number, please?
This trick works only in the US with 7digit phone numbers. Make sure you hit enter/equal between each step.

Open your iPhone calculator

Type in the first 3 digits of your phone number (not your area code) (So you would type in 759 if your number was 8017591234)

Multiply that number by 80 (759 x 80 = 60,720)

Add 1 (60,720 + 1 = 60,721)

Multiply by 250 (60,721 x 250 = 15,180,250)

Add last four digits of your phone number (15,180,250 + 1234 = 15,181,484)

Add last four digits of your phone number again (15,181,484 + 1234 = 15,182,718)

Subtract 250 (15,182,718  250 = 15,182,468)

Divide number by 2. (15,182,468 ÷ 2 = 7,591,234  which is your phone number!)
The Secret of 73
This trick makes it appear that you can predict the future. Give it a whirl and see if it impresses a crowd.

Write the number 73 on a piece of paper, fold it up, and give it to an unsuspecting friend.

Tell your friend select a fourdigit number and enter it twice into a calculator.

Inform your friend that the number is divisible by 137 and ask him or her to verify using the calculator.

Tell your friends to divide the result by the original fourdigit number.

Astound your friend by asking him or her to unfold the paper. Voila! The answer on the calculator should match the number on the paper  73!
The Human Calculator, aka the 371337 Trick
This trick will make it appear that you are the world's fastest human calculator. To make it realistic, hand friend the iOS calculator and grab a piece of paper and pencil for yourself.
 Have your friend pick any 2 digit number (82, for example)
 Tell your friend to multiply this number by 3 and hit enter/equal (82 x 3 = 246)
 Then multiply that result by 7 and hit enter/equal (246 x 7 = 1,722)

Then multiply that result by 13 and hit enter/equal (1722 x 13 = 22,386)

Then multiply that result by 37 and hit enter/equal (22386 x 37 = 828,282)

While you friend is typing numbers furiously on your iPhone, you can write down the first number three times and find the answer in a matter of seconds. (828282 = 828282= 828,282)
Guess The Numbers!
This trick requires some work on your part. Just do the quick math at the end to baffle your friends with your math prowess.

Ask your friend to select two numbers, each of which is less than 10. (8 and 5, for example)

Tell your friend to choose either of the numbers and to multiply it by 5. (8 x 5 = 40)

Then tell your friend to add 7 to this result. (40 + 7 = 47)

Multiply the resulting sum by 2. (47 x 2 = 94)

Add it to the other number that was first selected. (94 + 5 = 99)

Have your friend tell you the result. (The answer is 99!)

Now it is your turn. Take your friend's answer and subtract 14. You should get a two digit number  the digit in the ten's place is the number that was multiplied by 5 and the digit in the one's place is the other number chosen at the beginning. (99  14 = 85)
Find The Deleted Digit
Like the "Guess The Numbers" above, this trick requires some quick calculating on your part. Just do the calculation at the end, and you'll have your friends scratching their head wondering how you did that.

Ask your friend to write down any number that is at least four digits long. Ask them to hide it, so you can't see it. (4798, for example)

Tell your friend to add the individual digits (4 + 7 + 9 + 8 = 109)

Then tell them to subtract that answer from the first number (4789  109 = 4680)

Tell your friend to cross out one digit from this answer. It can be any digit they want, except zero. (Let's cross out 6, so 4680 becomes 4x80)

Ask your friend to read out the remaining digits (He or she should say 480)

Now it is your turn to do some math. Add up the digits your friend just read aloud (4 + 8 + 0 = 12). Find the next highest number that is divisible by 9. (18, in this case). Subtract your sum (12) from the number that can be divided by 9, (18  12 = 6). The result (6) is the value of the digit that was crossed out.
Age By Chocolate
This is an oldie, but goodie. Its hook is the chocolate theme  who can resist the allure of this sweet treat, even if it means revealing your age?

Tell your friend to select the number of times a week that they would like to have chocolate. The number has to be more than one, but less than 10. Use some cajoling to get them to pick a number in that range. (Let's say it is 6 times a week, for example)

Multiply this number by 2 (6 x 2 = 12)

Add 5 to the result (12 + 5 = 17)

Break out the chocolate calculator to multiply the result by 50 (17 x 50 = 850)

Ask your friend if they already had their birthday this year. If they did, then tell them to add 1763 to their result. If they haven't, then tell them to add 1762. (850 + 1763 = 2613) Note: These numbers (1763, 1762) make the trick work in the year 2013. Use 1764 and 1763 in 2014.

Now subtract the four digit year of their birthday. (2613  1970 = 643)

The resulting value will be a three digit number (643). The hundred's place will be the number of times per week you want chocolate (6!), while the remaining digits will reveal your age (43yo)!
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