What is the value of the variable X in the equation as shown in the figu...
Friday, March 26, 2010
Divide by Parts
Divide 110 into two parts so that one will be 150 percent of the other. What are the 2 numbe...
Is A Guilty?
There was a robbery in which a lot of goods were stolen. The robber(s) left in a truck. It is known that : (1) Nobody else could have been involved other than A, B and C. (2) C never commits a crime without A's participation. (3) B does not know how to drive. So, is A innocent or guil...
Who is in the picture?
Stephen was looking at a photo. Someone asked him, "Whose picture are you looking at?" He replied: "I don't have any brother or sister, but this man's father is my father's son." So, whose picture was Stephen looking ...
Order Finder
Isaac and Albert were excitedly describing the result of the Third Annual International Science Fair Extravaganza in Sweden. There were three contestants, Louis, Rene, and Johannes. Isaac reported that Louis won the fair, while Rene came in second. Albert, on the other hand, reported that Johannes won the fair, while Louis came in second. In fact, neither Isaac nor Albert had given a correct report of the results of the science fair. Each of them had given one correct statement and one false statement. What was the actual placing of the three contestan...
Immortal wars
the war is legend and myth it was started in temples the three opposing leaders were siblings by magic blood one ruled the ocean other the sky last the dead they were in times of ancient each wants the throne what and who are the three opposing leaders and what throne are they fighting over?...
Friday, March 5, 2010
The 11 Rule
You likely all know the 10 rule (to multiply by 10, just add a 0 behind the number) but do you know the 11 rule? It is as easy! You should be able to do this one in you head for any two digit number. Practice it on paper first!To multiply any two digit number by 11: For this example we will use 54. Separate the two digits in you mind (5__4). Notice the hole between them! Add the 5 and the 4 together (5+4=9) Put the resulting 9 in the hole 594. That's it! 11 x 54=594 The only thing tricky to remember is that if the result of the addition is greater than 9, you only put the "ones" digit in the hole and carry the "tens" digit from the addition. For example 11 x 57 ... 5__7 ... 5+7=12 ... put the 2 in the hole and add the 1 from the 12 to the 5 in to get 6 for a result of 627...
Squaring a 2-digit number ending in 8
Choose a 2-digit number ending in 8. The last digit of the answer is always 4: _ _ _ 4 Multiply the first digit by 6 and add 6 (keep the carry): _ _ X _ Multiply the first digit by the next consecutive number and add the carry: the product is the first two digits: XX _ _. Example: If the number is 78: The last digit of the answer is 4: _ _ _ 4 Multiply the first digit (7) by 6 and add 6 (keep the carry): 7 × 6 = 42, 42 + 6 = 48; the next digit of the answer is 8 (keep carry 4): _ _ 8 4 Multiply the first digit (7) by the next number (8) and add the carry (4): 7 × 8 = 56, 56 + 4 = 60 (the first two digits): 6 0 _ _ So 78 × 78 = 6084. See the pattern? For 38 × 38 The last digit of the answer is 4: _ _ _ 4 Multiply...
Squaring a 2-digit number ending in 7
Choose a 2-digit number ending in 7. The last digit of the answer is always 9: _ _ _ 9 Multiply the first digit by 4 and add 4 (keep the carry): _ _ X _ Multiply the first digit by the next consecutive number and add the carry: the product is the first two digits: XX _ _. Example: If the number is 47: The last digit of the answer is 9: _ _ _ 9 Multiply the first digit (4) by 4 and add 4 (keep the carry): 4 × 4 = 16, 16 + 4 = 20; the next digit of the answer is 0 (keep carry 2): _ _ 0 9 Multiply the first digit (4) by the next number (5) and add the carry (2): 4 × 5 = 20, 20 + 2 = 22 (the first two digits): 2 2 _ _ So 47 × 47 = 2209. See the pattern? For 67 × 67 The last digit of the answer is 9: _ _ _ 9 Multiply...
Squaring a 2-digit number ending in 6
Choose a 2-digit number ending in 6. Square the second digit (keep the carry): the last digit of the answer is always 6: _ _ _ 6 Multiply the first digit by 2 and add the carry (keep the carry): _ _ X _ Multiply the first digit by the next consecutive number and add the carry: the product is the first two digits: XX _ _. Example: If the number is 46, square the second digit : 6 × 6 = 36; the last digit of the answer is 6 (keep carry 3): _ _ _ 6 Multiply the first digit (4) by 2 and add the carry (keep the carry): 2 × 4 = 8, 8 + 3 = 11; the next digit of the answer is 1: _ _ 1 6 Multiply the first digit (4) by the next number (5) and add the carry: 4 × 5 = 20, 20 + 1 = 21 (the first two digits): 2 1 _ _ So 46 × 46 = 2116. ...
Squaring a 2-digit number ending in 5
Choose a 2-digit number ending in 5. Multiply the first digit by the next consecutive number. The product is the first two digits: XX _ _. The last part of the answer is always 25: _ _ 2 5. Example: If the number is 35, 3 × 4 = 12 (first digit times next number). 1 2 _ _ The last part of the answer is always 25: _ _ 2 5. So 35 × 35 = 1225. See the pattern? For 65 × 65, 6 × 7 = 42 (first digit times next number): 4 2 _ _. The last part of the answer is always 25: _ _ 2 5. So 65 × 65 = 4225. ...
Thursday, March 4, 2010
Folded sheet of paper
A rectangular sheet of paper is folded so that two diagonally opposite corners come together. If the crease formed is the same length as the longer side of the sheet, what is the ratio of the longer side of the sheet to the shorter si...
Painted cubes
Twenty-seven identical white cubes are assembled into a single cube, the outside of which is painted black. The cube is then disassembled and the smaller cubes thoroughly shuffled in a bag. A blindfolded man (who cannot feel the paint) reassembles the pieces into a cube. What is the probability that the outside of this cube is completely bla...
Squaring a 2-digit number ending in 5
Choose a 2-digit number ending in 5. Multiply the first digit by the next consecutive number. The product is the first two digits: XX _ _. The last part of the answer is always 25: _ _ 2 5. Example: If the number is 35, 3 × 4 = 12 (first digit times next number). 1 2 _ _ The last part of the answer is always 25: _ _ 2 5. So 35 × 35 = 1225. See the pattern? For 65 × 65, 6 × 7 = 42 (first digit times next number): 4 2 _ _. The last part of the answer is always 25: _ _ 2 5. So 65 × 65 = 4225. ...
Squaring a 2-digit number ending in 4
Take a 2-digit number ending in 4. Square the 4; the last digit is 6: _ _ _ 6 (keep carry, 1.) Multiply the first digit by 8 and add the carry (1); the 2nd number will be the next to the last digit: _ _ X 6 (keep carry). Square the first digit and add the carry: X X _ _. Example: If the number is 34, 4 × 4 = 16 (keep carry, 1); the last digit is _ _ _ 6. 8 × 3 = 24 (multiply the first digit by 8), 24 + 1 = 25 (add the carry): the next digit is 5: _ _ 5 6. (Keep carry, 2.) Square the first digit and add the carry, 2: 1 1 5 6. So 34 × 34 = 1156. See the pattern? For 84 × 84, 4 × 4 = 16 (keep carry, 1); the last digit is _ _ _ 6. 8 × 8 = 64 (multiply the first digit by 8), 64 + 1 = 65 (add the carry): the next digit...
Three simultaneous equations
Find all positive real solutions of the simultaneous equations: x + y2 + z3 = 3y + z2 + x3 = 3z + x2 + y3 =...
Fermatt's squares
By Fermat's Little Theorem, the number x = (2p−1 − 1)/p is always an integer if p is an odd prime. For what values of p is x a perfect squa...
Compute this series?
Compute the infinite product [sin(x) cos(x/2)]1/2 · [sin(x/2) cos(x/4)]1/4 · [sin(x/4) cos(x/8)]1/8 · ... , where 0 x ...
Squaring a 2-digit number ending in 4
Take a 2-digit number ending in 4. Square the 4; the last digit is 6: _ _ _ 6 (keep carry, 1.) Multiply the first digit by 8 and add the carry (1); the 2nd number will be the next to the last digit: _ _ X 6 (keep carry). Square the first digit and add the carry: X X _ _. Example: If the number is 34, 4 × 4 = 16 (keep carry, 1); the last digit is _ _ _ 6. 8 × 3 = 24 (multiply the first digit by 8), 24 + 1 = 25 (add the carry): the next digit is 5: _ _ 5 6. (Keep carry, 2.) Square the first digit and add the carry, 2: 1 1 5 6. So 34 × 34 = 1156. See the pattern? For 84 × 84, 4 × 4 = 16 (keep carry, 1); the last digit is _ _ _ 6. 8 × 8 = 64 (multiply the first digit by 8), 64 + 1 = 65 (add the carry): the next digit...
Squaring a 2-digit number ending in 3
Take a 2-digit number ending in 3. The last digit will be _ _ _ 9. Multiply the first digit by 6: the 2nd number will be the next to the last digit: _ _ X 9. Square the first digit and add the number carried from the previous step: X X _ _. Example: If the number is 43, the last digit is _ _ _ 9. 6 × 4 = 24 (six times the first digit): _ _ 4 9. 4 × 4 = 16 (square the first digit), 16 + 2 = 18 (add carry): 1 8 4 9. So 43 × 43 = 1849. See the pattern? For 83 × 83, the last digit is _ _ _ 9. 6 × 8 = 48 (six times the first digit): _ _ 8 9. 8 × 8 = 64 (square the first digit), 64 + 4 = 68 (add carry): 6 8 8 9. So 83 × 83 = 6889. ...
Squaring a 2-digit number ending in 2
Take a 2-digit number ending in 2. The last digit will be _ _ _ 4. Multiply the first digit by 4: the 2nd number will be the next to the last digit: _ _ X 4. Square the first digit and add the number carried from the previous step: X X _ _. Example: If the number is 52, the last digit is _ _ _ 4. 4 × 5 = 20 (four times the first digit): _ _ 0 4. 5 × 5 = 25 (square the first digit), 25 + 2 = 27 (add carry): 2 7 0 4. So 52 × 52 = 2704. See the pattern? For 82 × 82, the last digit is _ _ _ 4. 4 × 8 = 32 (four times the first digit): _ _ 2 4. 8 × 8 = 64 (square the first digit), 64 + 3 = 67 (add carry): 6 7 2 4. So 82 × 82 = 6724. ...
Squaring a 2-digit number ending in 1
Take a 2-digit number ending in 1. Subtract 1 from the number. Square the difference. Add the difference twice to its square. Add 1. Example: If the number is 41, subtract 1: 41 - 1 = 40. 40 × 40 = 1600 (square the difference). 1600 + 40 + 40 = 1680 (add the difference twice to its square). 1680 + 1 = 1681 (add 1). So 41 × 41 = 1681. See the pattern? For 71 × 71, subtract 1: 71 - 1 = 70. 70 × 70 = 4900 (square the difference). 4900 + 70 + 70 = 5040 (add the difference twice to its square). 5040 + 1 = 5041 (add 1). So 71 × 71 = 5041. ...
Squaring a 2-digit number beginning with 9
Take a 2-digit number beginning with 9. Subtract it from 100. Subtract the difference from the original number: this is the first part of the answer. Square the difference: this is the last part of the answer. Example: If the number is 96, subtract: 100 - 96 = 4, 96 - 4 = 92. The first part of the answer is 92 _ _ . Take the first difference (4) and square it: 4 × 4 = 16. The last part of the answer is _ _ 16. So 96 × 96 = 9216. See the pattern? For 98 × 98, subtract: 100 - 98 = 2, 98 - 2 = 96. The first part of the answer is 96 _ _. Take the first difference (2) and square it: 2 × 2 = 4. The last part of the answer is _ _ 04. So 98 × 98 = 9604. ...
Squaring a 2-digit number beginning with 5
Take a 2-digit number beginning with 5. Square the first digit. Add this number to the second number to find the first part of the answer. Square the second digit: this is the last part of the answer. Example: If the number is 58, multiply 5 × 5 = 25 (square the first digit). 25 + 8 = 33 (25 plus second digit). The first part of the answer is 33 3 3 _ _ 8 × 8 = 64 (square second digit). The last part of the answer is 64 _ _ 6 4 So 58 × 58 = 3364. See the pattern? For 53 × 53, multiply 5 × 5 = 25 (square the first digit). 25 + 3 = 28 (25 plus second digit). The first part of the answer is 28 2 8 _ _ 3 × 3 = 9 (square second digit). The last part of the answer is 09 _ _ 0 9 So 53 × 53 = 2809. ...
Squaring a 2-digit number beginning with 1
Take a 2-digit number beginning with 1. Square the second digit (keep the carry) _ _ X Multiply the second digit by 2 and add the carry (keep the carry) _ X _ The first digit is one (plus the carry) X _ _ Example: If the number is 16, square the second digit: 6 × 6 = 36 _ _ 6 Multiply the second digit by 2 and add the carry: 2 × 6 + 3 = 15 _ 5 _ The first digit is one plus the carry: 1 + 1 = 2 2 _ _ So 16 × 16 = 256. See the pattern? For 19 × 19, square the second digit: 9 × 9 = 81 _ _ 1 Multiply the second digit by 2 and add the carry: 2 × 9 + 8 = 26 _ 6 _ The first digit is one plus the carry: 1 + 2 = 3 3 _ _ So 19 × 19 = 361. ...
