2*(-7) = -14
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It means you double 7. So 7 * 2 = 14
The answer is 42. 14 + 7 = 21 21 x 2 = 42
Double the last digit and subtract the last digit from the remaining digits.
6+7
7: If you double the last digit and subtract it from the rest of the number and the answer is: 0 or Divisible by 7 (Note: you can apply this rule to that answer again if you want)Example: 1, 672 (Double 2 is 4, 67-4=63, and 63÷7=9) Yes2, 905 (Double 5 is 10, 90-10=80, and 80÷7=11 3/7) No8: The last three digits are divisible by 8Example: 1,109816 (816÷8=102) Yes 2,216302 (302÷8=37 3/4) No