Fraction problem nightmare?
"Seven Eigths of a set of shapes are regular polygons. Of the regular polygons, 1/5 are equilateral triangles. What fractions of the set are equilateral triangles?"...the book says 7 tenths is the answer, but how!?

answers:
geezer say: 7/8 are regular polygons
1/5 are equilateral triangles
7/8 x 1/5 = 7/40
It would be 7/10 if it was 4/5 are triangles
7/8 x 4/5 .. 28/40 .. 7/10

RR say: "Seven Eighths of a set of shapes are regular polygons.
7/8
Of the regular polygons, 1/5 are equilateral triangles.
7/8 x 1/5 = 7/40
The book must have a misprint!!

Krishnamurthy say: Seven Eighths of a set of shapes are regular polygons.
Of the regular polygons, 1/5 are equilateral triangles.
7/8 × 1/5 = 7/40
What fractions of the set are equilateral triangles?"
7 tenths is not the answer, but 7 fortieths is the answer.

Mike G say: Number in set = S
Number of regular polygons = P
Number of equilateral triangles = T
P = (7/8)S
T = (1/5)P = (1/5)(7/8)S = (7/40)S
Answer 7/40

Steve A say: Should say 4/5 are equilateral triangles.

llaffer say: Let x = total number of shapes.
we know that 7/8 of all the shapes are regular, so the number of regular polygons is: (7/8)x
Of these, 1/5 are triangles, so the number of triangles is: (7/8)(1/5)x = (7/40)x
I agree that (7/10) is incorrect. I get (7/40).
