Grades 4–8

Number Sense & Mental Math

Every shortcut here comes with a picture that shows why it works — usually an area model — and a test-ready write-up with the textbook reason.

Multiply 23 × 27 in 3 Seconds

30 s · Number Sense & Mental Math

Multiply 37 × 77 in 3 Seconds

38 s · Number Sense & Mental Math

×11 in 3 Seconds: Pull Apart, Add the Middle

1:38 · Number Sense & Mental Math

49 × 51 in Your Head? Cut One Strip and It's Easy

1:55 · Number Sense & Mental Math

Square Any Number Ending in 5 in Your Head (35², 75²…)

1:58 · Number Sense & Mental Math

Add 1 to 100 in Seconds: Gauss's Trick (With a Picture)

1:47 · Number Sense & Mental Math