Try the different numbers - there are only 11 after all - and multiply their digits. Or analyze the factors of the number 21.
it is 21?
Estimating the product of 68 and 21 . . . It is easy in your head to think that this product would be close to 70 times 20. Again, in your head, you can figure that product to be 1400.
The number is 490.
The factors of 21 are 1,3,7, and 21. The factors of 70 are 1,2,5,7,14,35, and 70.
The product of 70 and 40 = 70 x 40 = 2800.
80
The factors of 21 are 1,3,7, and 21. The factors of 70 are 1,2,5,7,14,35, and 70 The common factors of 21 and 70 are 1 and 7.
21 is 70% of 30.
70% of 21 is 70 hundredths of 21. One hundredth of 21 is 0.21 (1/100 x 21 = 0.21) So 70 hundredths is 70 times as much. That's 0.21 x 70 = 1470
70 is the product of (7)(2)(5)=70.
80 + 70 + 60 + 50 + 40 + 30 + 20 +10 = 360
LCM of 21 and 70 = 210