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# Multiplying 2 numbers starting with same digit

## on Jan 31, 2012

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## Multiplying 2 numbers starting with same digit Presentation Transcript

• Xtra Math: Methods, Tips And Tricks Series. By Puwork Utara May 2012
• Multiplying 2 NumbersStarting WithSame Digit(s)
• 1st Examination 16 X 13 = ___ if reference point is 10 Step 1 : Determine how much 16 from 10 and how much 13 from 10 -6 Means 16 is 6 more than 10 16 10 13 - 3 Means 13 is 3 more than 10 10 Step 2 : Either ( 16 - (-3) ) X 10 = 19 X 10 = 190 Or (-6) = ( 13 - ) X 10 19 X 10 = 190 Step 3 : ( -6 ) X ( -3 ) = 18 Step 4 : 190 + 18 = 208 # We just solved this using reference point method of the base 10
• 2nd Examination 16 X 13 = ___ if reference point is 20 Step 1 : Determine how much 16 from 20 and how much 13 from 20 +4 Means 16 is 4 less than 20 16 20 13 +7 Means 13 is 7 less than 20 20 Step 2 : Either ( 16 - ( + 7) ) X 20 = 9 X 20 = 180 Or ( + 4) = ( 13 - ) X 20 9 X 20 = 190 Step 3 : (+4) X ( + 7 ) = 28 Step 4 : 180 + 28 = 208 # We just solved this using reference point method of the base 20
• 3rd Examination 16 X 13 = ___ if reference point is 30 Step 1 : Determine how much 16 from 30 and how much 13 from 30 + 14 Means 16 is 14 less than 30 16 30 13 + 17 Means 13 is 17 less than 30 30 Step 2 : Either ( 16 - ) X 30 ( + 17) = -1 X 30 = - 30 Or ( 13 - ( + 14) ) X 30 = -1 X 30 = - 30 Step 3 : ( + 14 ) X ( +1 7 ) = 28 Step 4 : - 30 + 238 = 208 # We just solved this using reference point method of the base 30
• 9th Examination 16 X 13 = ___ if reference point is 90 Step 1 : Determine how much 16 from 90 and how much 13 from 90 + 74 Means 16 is 74 less than 90 16 90 13 + 77 Means 13 is 77 less than 90 90 Step 2 : Either ( 16 - ) X 90 ( + 77) = - 61 X 90 = - 5490 Or ( 13 - ( + 74) ) X 90 = - 61 X 90 = - 5490 Step 3 : ( + 74 ) X ( +77 ) = 5698 Step 4 : - 5490 + 5698 = 208 # The higher the base number the more difficult to solve the problem, but we still get the same result.
• So, here are the recommendation of reference point 11 to 19 use 10 as the Base Number 21 to 29 use 20 as the Base Number 31 to 39 use 30 as the Base Number 41 to 49 use 40 as the Base Number 51 to 59 use 50 as the Base Number 61 to 69 use 60 as the Base Number 71 to 79 use 70 as the Base Number 81 to 89 use 80 as the Base Number 91 to 99 use either 90 or 100 as the Base Number 101 – 109 use 100 as the Base Number