Helps you understand
Four operationsPlace value is what makes column addition, carrying and long division work.
Number system
How do we read, write and compare really big numbers — and why do Indians and the rest of the world put commas in different places?
Place value, number names, expanded form, predecessors and successors, the Indian and International systems, and rounding — the toolkit for every large number you will ever meet.
5 depths≈ 230 min of reading83 practice questions
The ladder
Choose how deep to go
Every depth is open. Start where it feels interesting — you can always move back.
- Discoverabout 35 minBig numbers all around usMeet place value through bundles of sticks, cricket crowds and rupee notes. Learn to read and write big numbers the Indian way (lakh, crore) and the international way (million, billion), find the number just before and after, compare, round and even read Roman numerals.Owner-accepted · not line-by-line reviewed
- Understandabout 45 minHow place value works, and how to use itExact rules for place and face value, expanded form, number names and both comma systems, with many worked examples. Then reliable methods for converting, comparing, ordering, forming numbers, rounding, estimating and Roman numerals, plus the mix-ups to avoid.Owner-accepted · not line-by-line reviewed
- Investigateabout 45 minTesting big-number ideasMake predictions about place value and then test them: what moving a digit does, how many numbers of each size exist, when a successor gains a digit, which numbers round to the same value, how far off an estimate can be, and why 6174 keeps appearing.Owner-accepted · not line-by-line reviewed
- Go deeperabout 50 minWhy place value worksPowers of ten, and proofs that the rules for comparing, rounding and forming numbers always work. Bound estimate errors, meet Sanskrit names for powers of ten, follow our digits from Brahmi to Aryabhata to Baghdad to Europe, and see metric units as place value.Owner-accepted · not line-by-line reviewed
- Extendabout 55 minBeyond a billion, and beyond base tenStretch the number system in every direction: bigger names in both systems, real Indian large numbers from elections to Mars, number systems of the Babylonians, Maya and Egyptians, binary as a place-value system, olympiad-style puzzles, Fermi estimates, projects and open questions.Owner-accepted · not line-by-line reviewed
Practise and apply
Question bank · 83 questions
9 sections from Foundation to Challenge, each with hints and a worked solution — or play a 10-question round for points and stars.
Foundation 20Core 30Stretch 22Challenge 11
The web
Connected ideas
Follow a connection when you’re curious — some lead into completely different areas.
Number system
Helps you understand
Data handlingReading, comparing and rounding numbers comes first when you sort data and round a mean.
Related to
Number and shape patternsPlace-value charts are full of patterns: each place is ten times the one to its right.
Used inanother area
ElectricityPower stations are rated in megawatts and India uses lakhs of crores of units a year: reading such numbers needs place value and the Indian system.
Usesanother area
How government works in IndiaElection results and budgets are read in lakhs and crores — place value with real consequences.
Words to know
57 words are explained in these lessons
DigitPlacePlace valueFace valueExpanded formPeriodLakhCroreMillionBillionSuccessorPredecessor+45 more