18)
The Last case is 252 because 28 * 9 = 252.
Second Case is 9 because 8*9 = 72, and 252 - 72 = 180, then you divide 180 over 20, and you get 9.
So, 28 * 9 = 20 * 9 + 8 * 9 = 252
19)
in Math, when they say "of", it means you need to multiply, so you get:
[tex] \frac{4}{7} * 98[/tex]
do it on the calculator and you get 56.
20)
To add fractions, they need to have the same denominator. Since here they got the same (10), you get:
[tex] \frac{6}{10} + \frac{1}{10} + \frac{4}{10} [/tex]
[tex] \frac{6+1+4}{10} [/tex]
[tex] \frac{11}{10} [/tex]
Hope this Helps! :D
