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SQUARING 5 MULTIPLES WITHOUT A CALCULATOR

Fast way  to square multiples of 5 e.g. 5,15,25,35,105,115 etc.
  1. First break the number into two digits
  2. multiply the first number by the next natural digit
  3. Then square 5 and write together with the product of the numbers.

See exercise below
Number
Square
Operation
5
25
5 is 05 , 0 x 1 and 52 , 25. Combining  gives 25. Confused let look at another one
15
225
15 is 1 and 5.Next number after 1 is 2 So 1 x 2 = 2, while 52 = 25. Combining gives 225.
25
625
25 is 2 and 5.Next number after 2 is 3 So 2 x 3 = 6, while 52 = 25. Combining gives 625.
35
1225
35 is 3 and 5.Next number after 3 is 4 So 3 x 4 = 12, while 52 = 25. Combining gives 1225.
125
15625
125 is 12 and 5.Next number after 12 is 13 So 12 x 13 = 156, while 52 = 25. Combining gives 15625.

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