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#31135
Shikha Dhingra
Participant

Challenge Question #11

47 X 67   As in lesson 17 the digits at tens place are same and  the sum of digits at ones place is 10  we try to convert digits according to that.

47  X (100-33 )

47 X(100 – 33 + 10 -10)                    adding +10 and -10  so that (-33 -10) becomes -43

47 X(100 -43 +10)

4700 -(47 X43) + (47 X10)                now  in   47 X43   the digits at tens place are same and sum of digits at ones place is 10

4700 – 2021 +470  =5170 -2021 =3149

 

  94 X 67              2 X 47 X 67

2 X (3149) =      6298              multiplication of 47 and 67 is same as above

32 X36        multiply by 2

2 X 32 X 36= 64 X36

= (64 -30 +30 ) X36           adding +30 and -30  to make ( 64-30 = 34)

=  (34  +30 ) X36

= 34 X36 + ( 30 X 36)            now in 34 and 36 the tens digits are same and sum of ones digits is 10

= 1224 + 1080 = 2304

now divide by 2 as we have multiply by 2  in the beginning

therefore 2304 ÷ 2 = 1152

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