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Puzzles
Twenty
Source:
UKMT Junior Mathematical Olympiad 2013
How many three digit integers are there for which the product of the digits is 20?
Show answer & extension
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There are two ways to make 20 by multiplying three digits:
2
×
2
×
5
and
1
×
4
×
5
. Listing all the possible orderings of these, we have:
145
154
415
451
514
541
225
252
522
Therefore, there are 9 different three digit numbers where the product of the digits is 20.
Extension
How many 4 digit numbers are there where the product of the digits is 20?
5 digit?
n
digit?
Tags:
numbers
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sums
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trigonometry
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prime numbers
volume
spheres
christmas
integration
lines
advent
differentiation
numbers grids
chocolate
the only crossnumber
scales
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geometry
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cryptic crossnumbers
area
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grids
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2d shapes
triangles
decahedra
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percentages
arrows
planes
angles
time
tangents
fractions
pentagons
money
multiples
3d shapes
rectangles
star numbers
addition
ellipses
crosswords
combinatorics
coordinates
partitions
surds
speed
pascal's triangle
coins
axes
tournaments
folding tube maps
triangle numbers
algebra
ave
mean
crossnumbers
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calculus
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dominos
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