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Gyaan Maths
CBSE · Class 6-12
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Class 8 · Ganita Prakash
Unit 5 · Class 8Ganita Prakash
Number Play
Number puzzles, divisibility, and digit patterns.
Lessons
3 concepts
1
Combined Rules
Divisible by 6 = by 2 AND 3. By 12 = by 3 AND 4. Combining rules speeds up checks.
2
Cryptarithms
Letters stand for digits. Systematic elimination and divisibility narrow down possibilities.
3
Digit Reversal
For 2-digit
a
b
‾
\overline{ab}
ab
:
10
a
+
b
10a+b
10
a
+
b
; reversed
10
b
+
a
10b+a
10
b
+
a
; difference
9
(
a
−
b
)
9(a-b)
9
(
a
−
b
)
— always divisible by 9.
Skills to practise
Skill · medium
Number Play — Practice