Write an expression 13+ 19+ 17 using mental math

Explanation:

It is convenient to regroup the numbers, and adjust two of them to "make a ten".

  = 13 + 17 + 19 . . . . rearrange (swap the order of 17 and 19)

  = (10 + 3) + (-3 + 20) + 19 . . . . "make a ten" by adding or subtracting a small number. Here, those adjustments cancel—which is the point of doing it.

  = 10 + 20 + 19

  = 30 + 19

  = 49

Hey!

Weight of small box = 5 lb. x no. of small boxes total weight = 5*x

Weight of Large boxes = 12 lb. y no. of large boxes total weight = 12*y

Total weight = 5x + 12y.

Since total weight carrying capacity of shelf is 80, thus the inequality becomes:

5x + 12y Less than or equal to 80.

(a) satisfies the inequality.

(b) satisfies the inequality.

Hope my answer helps!