2D base 10 blocks, popularly known as Flats-Longs-Units (FLU) are the most useful of all manipulatives for numbers. They can be extended to decimals through fractions as well as to algebra tiles.

These pre-grouped proportional manipulatives can be used to introduce numbers up to 999 and the four operations - addition, subtraction, multiplication and division. In fact, they can be used to understand the division algorithm to find the square root!

Cryptography is the science of making and breaking codes. Ciphers are methods for transforming a given message, the
plaintext, into a new form (ciphertext) unintelligible to anyone who does not know the key. In this article we explore an interesting cryptography method known as the Hill Cipher, based on matrices. We explore the method using the spreadsheet MS Excel to perform operations on matrices.
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