Class 8 Maths: Quadrilaterals, Data Handling, Squares, Cubes & Comparing Quantities: quick revision, 18 bites

The Angle-Sum Rule That Unlocks Every Quadrilateral

All quadrilaterals hide the same 360°.

Every quadrilateral — square, rectangle, trapezium, kite, parallelogram — has interior angles that add up to **360°**. This single rule solves most angle-finding problems.

Takeaway. If you know three angles of any quadrilateral, the fourth is 360° minus their sum.

Quadrilateral Family: Who Inherits What

A square is a rectangle — but not always.

Takeaway. Square ⊂ Rhombus ⊂ Parallelogram and Square ⊂ Rectangle ⊂ Parallelogram.

Diagonals: Equal vs Bisecting vs Perpendicular

Don't mix up which shape does what.

Takeaway. Only the square has all three diagonal properties: bisect, equal, perpendicular.

Exterior Angle of a Polygon — The 360° Shortcut

Exterior angles always sum to 360°.

Takeaway. Use 360°/n for exterior angles — faster than the (n−2)×180 formula for regular polygons.

Mean, Median, Mode — Three Averages, Three Jobs

One outlier can wreck the mean.

Takeaway. Mean uses all values; median resists outliers; mode shows the most frequent.

Drawing a Bar Graph vs a Double Bar Graph

Two datasets? Use a double bar.

Takeaway. Equal bar widths, equal gaps, uniform scale — these three make a bar graph correct.

Probability: From 0 to 1, Nothing Outside

Probability never leaves the 0–1 zone.

Takeaway. If your probability answer is >1 or <0, you've made an error — recheck the count.

Perfect Squares: The Two Must-Know Identities

These two identities save minutes.

Takeaway. Split any number near a multiple of 10 and apply (a±b)² to square it mentally.

Perfect Squares Never End in These Digits

No square ends in 2, 3, 7, or 8.

Takeaway. Check the last digit first — it eliminates most non-squares instantly.

Square Root by Prime Factorisation — Step by Step

Pair the primes, take one out.

Takeaway. Prime factorisation + pairing = reliable square root for any perfect square.

Smallest Number to Multiply/Divide for a Perfect Square

Unpaired primes are the culprit.

Takeaway. Multiply/divide by the product of unpaired primes to reach the nearest perfect square.

Cube Roots: Group Primes in Triples

Triples, not pairs, for cubes.

Takeaway. Cube root = prime factorisation with groups of three.

Cubes: Last Digit Tells You the Root's Last Digit

Ends in 8? Root ends in 2.

Takeaway. The last digit of a cube uniquely determines the last digit of its cube root.

Profit, Loss & Discount — The Three Formulas

CP, SP, MP — know your base.

Takeaway. Profit/loss → base is CP. Discount → base is MP. Never swap them.

Simple vs Compound Interest — One Formula Difference

SI adds flat; CI compounds.

Takeaway. SI grows linearly; CI grows on the new amount each year.

2-Day Revision Plan for These 5 Chapters

Two days, five chapters, one plan.

Takeaway. Formula sheet + NCERT problems + one mock = maximum marks in minimum time.

Remember Square Roots 1–30 in One Go

Chant the squares, own the roots.

Memorising squares up to 30 makes square-root questions near-instant. Use rhythm: 1, 4, 9, 16, 25, 36, 49, 64, 81, 100…

Takeaway. Squares 1–30 memorised = faster square roots and factorisation.

Where These Chapters Show Up in Real Life

Maths you'll actually use tomorrow.

Takeaway. Every chapter here is a tool you'll use outside the exam hall.