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To find out if a number is divisible by seven:
Take the last digit, double it, and subtract it from the rest of the
number.
If the answer is more than a 2 digit number perform the above
again.
If the result is 0 or is divisible by 7 the original number is also
divisible by 7.
Example 1 ) 259
9*2= 18.
2518 = 7 which is divisible by 7 so 259 is also divisible by 7.
Example 2 ) 2793
3*2= 6
2796= 273
now 3*2=6
276= 21 which is divisible by 7 so 2793 is also divisible by 7 .
Now find out if following are divisible by 7
1) 2841
2) 3873
3) 1393
4) 2877
TO FIND SQUARE OF A NUMBER BETWEEN 40 to 50
Sq (44) .
1) Subtract the number from 50 getting result A.
2) Square A getting result X.
3) Subtract A from 25 getting result Y
4) Answer is xy
EXAMPLE 1 : 44
5044=6
Sq of 6 =36
256 = 19
So answer 1936
EXAMPLE 2 : 47
5047=3
Sq 0f 3 = 09
253= 22
So answer = 2209
NOW TRY To Find Sq of 48 ,26 and 49
TO FIND SQUARE OF A 3 DIGIT NUMBER :
LET THE NUMBER BE XYZ
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View Full Document SQ (XYZ) is calculated like this
STEP 1. Last digit = last digit of SQ(Z)
STEP 2. Second Last Digit = 2*Y*Z + any carryover from STEP 1.
STEP 3. Third Last Digit 2*X*Z+ Sq(Y) + any carryover from STEP
2.
STEP 4. Fourth last digit is 2*X*Y + any carryover from STEP 3.
STEP 5 . In the beginning of result will be Sq(X) + any carryover
from Step 4.
EXAMPLE :
SQ (431)
STEP 1. Last digit = last digit of SQ(1) =1
STEP 2. Second Last Digit = 2*3*1 + any carryover from STEP
1.= 6
STEP 3. Third Last Digit 2*4*1+ Sq(3) + any carryover from STEP
2.= 2*4*1 +9= 17. so 7 and 1 carryover
STEP 4. Fourth last digit is 2*4*3 + any carryover (which is 1) . =
24+1=25. So 5 and carry over 2.
STEP 5 . In the beginning of result will be Sq(4) + any carryover
from Step 4. So 16+2 =18.
So the result will be 185761.
If the option provided to you are such that the last two digits are
different, then you need to carry out first two steps only , thus
saving time. You may save up to 30 seconds on each
calculations and if there are 4 such questions you save 2
minutes which may really affect UR Percentile score.
PYTHAGORAS THEROEM :
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This note was uploaded on 01/27/2010 for the course EE 100 taught by Professor Abc during the Spring '10 term at Punjab Engineering College.
 Spring '10
 abc

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