399+428 make a ten or hundred to add mentally

827

Step-by-step explanation:

Hi there!

For any addition and subtraction, if you add and subtract 1 (or any other number), the result remains the same. In this case

399 + 428 = 399 + 428 + 1 - 1

Reordering

(399 + 1) + (428 -1)

Which gives

400 + 427

Which can easily solve to get 827

so a parallelogram is just like a square base times height. multiply 40 and 39 to get 1560 inches.

a triangle is base times height divided by two. so multiply 7.9 and 5 and then divide it by 2 to get 19.75inches.

the kite can be split into two separate triangles and added together to get the total area. 30 x 4 /2 which equals 60. make sure to double it for the two triangles making 120.

idk

step-by-step explanation: