Answer:
98 π R
Step-by-step explanation:
Surface area of sphere = 4 π R²
= 2 π R × 2 R
= 49 π × 2 R
= 98 π R
Answer:
C. 2.0 < t < 2.5
Step-by-step explanation:
time = distance / speed
The circumference of the lake is given by ...
C = πd = 2π miles ≈ 6.28 miles
Then Johanna's time is ...
(6.28 mi)/(3 mi/h) ≈ 2.09 h
This time is in the interval (2, 2.5), so matches choice C.
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<em>Alternate solution</em>
If we take pi to be 3, then this boils down to ...
2×3/3 = 2 . . . hours
Pi is on the order of 5% more than 3, so her time will be on the order of 5% more than 2 hours, or just above 2, but not as great as 2.5 hours. This sort of estimating can get you to the correct answer without a calculator.
Answer:
30% students
Step-by-step explanation:
Let x be the number of total students of a school.
63% are girls then total number of girls = (0.63)x
37% are boys then total number of boys = ( 0.37)x
Now 23% of girls wear contacts then total number of girls
= (0.63x) × 0.23
= (0.1449x)
And 42% of boys wear contacts then total number of boys wearing contacts
= (0.37x) ( 0.42)
= (0.1554)x
Total students wears contacts = ( 0.1449x) + (0.1554x)
= (0.3003x)
Percentage of students wear contacts = 
× 100
= 
× 100
= 30%
All 30% students wear contacts.
87 and 93
45 and 135
74 and 106
