Mental Math · Multiplication · M2
Some multipliers have shortcuts built from place value and halving. ×10 adds a zero. ×5 is ×10 then halve. ×50 is ×100 then halve. ×25 is ×100 then quarter. Each one trades a hard times-table for an easy slide-and-halve.
Watch the method
5 is half of 10. So 48 × 5 = 48 × 10 ÷ 2 = 480 ÷ 2 = 240. Multiplying by ten is easy, and halving is easy.
Multiply by 10 — just add a zero.
5 is half of 10, so halve it.
Your turn
Use the method, then check. Stuck? Reveal the steps.
×5 = ×10 then ÷2. ×50 = ×100 then ÷2. ×25 = ×100 then ÷4 (halve twice). You replace an awkward multiplier with a round one plus a halving.
Why it works
Five is half of ten; fifty is half of a hundred; twenty-five is a quarter of a hundred.
24 × 5
×10
24 × 10 = 240.
Halve
240 ÷ 2 = 120.
18 × 50
×100
18 × 100 = 1800.
Halve
1800 ÷ 2 = 900.
24 × 25
×100
24 × 100 = 2400.
Quarter
2400 ÷ 4 = 600.
Multiplying by 5 directly digit-by-digit.
It's faster to ×10 then halve. 48 × 5 → 480 → 240, no carrying.
Forgetting ×25 needs halving TWICE.
×25 = ×100 ÷ 4. Quarter means halve, then halve again.
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t₁ = 5, d = 3 and t1=5,d=3 both count. For a list of numbers, separate them with commas (e.g. 3, 10, 17).24 × 5 = ?
48 × 5 = ?
16 × 5 = ?
32 × 5 = ?
12 × 50 = ?
18 × 50 = ?
12 × 25 = ?
16 × 25 = ?
24 × 25 = ?
28 × 25 = ?
36 × 50 = ?
44 × 5 = ?