Answer:
32
Explanation:
In your head: 1/5 of 40 is 8 (since you know 5×8 = 40). Then 4 times that is 32 (since you know 4×8 = 32).
Your calculator can do this, too.
(4/5)·40 = 32
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In decimal, it is 0.8 · 40 = 8·4 = 32. Some folks are taught to do this sort of multiplication by taking a factor of 10 from one number and applying it to the other number. That is ...
... 0.8 × (10 × 4) = (0.8 ×10) × 4
... = 8 × 4 = 32
You can do substantially the same thing with the fraction.
... (4/5) × (5 × 8) = (4/5 × 5) × 8
... = 4 × 8 = 32