Answer:
Her electric toothbrush makes 210,000 rotations in one week
Explanation:
Note that:
∵ Gerry brushes her teeth for two minutes, twice a day
→ Twice means times 2
∴ Gerry brushes her teeth for 2 × 2 = 4 minutes a day
∵ Gerry's electric toothbrush rotates the brush 125 times per second
∵ 1 minute = 60 seconds
→ Multiply 125 by 60 to find the number of rotating in 1 minute
∴ Gerry's electric toothbrush rotates 125 × 60 = 7,500 in 1 minute
∵ Gerry brushes her teeth for 4 minutes a day
→ Multiply it by 4 to find the number of rotation in 1 day
∴ Gerry's electric toothbrush rotates 7,500 × 4 = 30,000 in 1 day
∵ 1 week = 7 days
→ Multiply the number of rotation in 1 day by 7 to find it in 1 week
∴ Gerry's electric toothbrush rotates 30,000 × 7 = 210,000 in 1 week
∴ Her electric toothbrush makes 210,000 rotations in one week