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December 22, 2014

December 22, 2014

Posted by **Max** on Wednesday, October 17, 2012 at 9:45am.

The ratio of the number of boys to that of girls in Class A is 2:3. The ratio of the number of girls who wear glasses to the number of girls who do not wear glasses is 1:3. If there are 12 more girls than boys, how many girls wear glasses?

The average height of 3 girls is 150cm. The heights of two of them are 1.6 m and 1.47 m. What is the height of the third girl?

A regular tank 40cm by 20cm by 20cm is filled with water up to 2/5 of its height. Water from a tap flows into the tank at 2.5 liters a minute. How much water is in the tank after 3 minutes? Give your answer in liters. (1Liter= 1000cm3)

- Maths -
**Jennifer**, Wednesday, October 17, 2012 at 10:23amGB = 8*G

BB = 3*B

GB - BB = 46

Where GB is the number of girl's books, BB is the number of boy's books, G is the number of girls, and B is the number of boys.

Use algebra to solve this system of equations

2nd problem

B/G = 2/3

G(glasses) + G(noglasses) = G

G(glasses)/G(noglasses) = 1/3

G - B = 12

where B is number of boys, G is number of girls, G(glasses) is number of girls with glasses, G(noglasses) is number of girls without glasses

Use algebra to solve this system of equations

3rd question:

1.6 m = 160 cm; 1.47 m = 147 cm

(160 + 147 + x) / 3 = 150

where x is the height of the third girl. Solve for x

4th question

The water in the tank before the tap turns on is

2/5 * 40 * 20 * 20 = 3200 cm3 = 3.2 L

After three minutes, 2.5 * 3 = 7.5 L

The total amount of water in the tank is 3.2 L + 7.5 L

- Maths -
**Reiny**, Wednesday, October 17, 2012 at 11:02am1. number of girls ---- x

number of boys --- 36-x

8x - 3(36-x) = 46

8x - 108 + 3x = 46

11x = 154

x = 14

There are 14 girls in the class

2. number of boys = 2x

number of girls = 3x

1/4 of the girls wear glasses, or

(3/4)x girls wear glasses

"there are 12 more girls than boys" ---> x - (36-x) = 12

2x = 48

x = 24

There are 24 girls , and 1/4 of those wear glasses**Then 6 girls wear glasses**

check:

24 girls and 12 boys, ratio is 12:24 = 2:3 , checks

1/4 of the 24 girls wear glasses ---> 6 girls wear glasses

ratio of glassed girl to non-glassed girls = 6 : 18 = 1:3 , checks

All is good!

3. (x+1.6+1.47)/3 = 1.50

x+1.6+1.47 = 4.5

x = 1.43

Third girl is 1.43 m or 143 cm tall

4. rate of flow = 2.5 L/min

after 3 minutes new amount of water = 3(2.5) = 7.5 L

plus the (2/5)(40)(20)(20) or 6400 mc^3 or 6.4 L already in tank

gives us 13.91 L

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