PROBABILITY F1

 

A bag contains 4 red balls and 8 blue balls. Two balls are taken from the bag. What is the probability that they are both red?

 

Solution

 

(This is a problem with replacement)

 

n(R) = 4, n(B) = 8, n(S) = 12

 

P(R) = n(R)

            n(S)

 

P(R) = 4

          12

 

1st pick = ⁴/12

2nd pick = ⁴/12 as well.

 

 

P(RR) =  4      x    4

             12            12

 

P(RR) =   ¹⁶ /144 = ¹/9       

 

Therefore Probability of drawing a red ball is 1/9     

 

 

TRY THIS ..............

 

A bag contains 7 purple stones and 11 yellow stones. Two stones are taken from the bag. What is the probability that they are both purple?

ALGEBRA 3F

 The sum of four consecutive even numbers is 316. Find the 3rd number.

 

Solution

 

Let the numbers be as shown in the table below

 

1st number	2nd number	3rd number	4th number	TOTAL
n	n+2	n+4	n+6	316

 

Then, n + (n+2) + (n+4) + (n+6) = 316

 

4n + 2+4+6= 316

 

4n + 12 = 316

 

4n = 316 – 12

 

4n = 304 

 

4n = 304

 4        4

 

n = 76

 

3rd number = n +4

 

                   = 76 + 4

 

                   = 80

 

Hence the 3rd number is 80

 

TRY THIS………………….. 

 

The sum of four consecutive even numbers is 372. Find the largest number.

ALGEBRA F3

 The sum of four consecutive even numbers is 316. Find the 3rd number.

 

Solution

 

Let the numbers be as shown in the table below

 

1st number	2nd number	3rd number	4th number	TOTAL
n	n+2	n+4	n+6	316

 

Then, n + (n+2) + (n+4) + (n+6) = 316

 

4n + 2+4+6= 316

 

4n + 12 = 316

 

4n = 316 – 12

 

4n = 304 

 

4n = 304

 4        4

 

n = 76

 

3rd number = n +4

 

                   = 76 + 4

 

                   = 80

 

Hence the 3rd number is 80

 

TRY THIS………………….. 

 

The sum of four consecutive even numbers is 372. Find the largest number.

LOGARITHMS F9

 Evaluate Log1,000,000,000 -  log 0.01 + log₃243

 

Solution

 

= Log1,000,000,000 -  log 0.001 + log₃243

 

= Log10⁹ -  log 10^-3 + log₃3^-5

 

= 9Log10 -  (-3log 10) + (-5log₃3)

 

= (9x1) - (-3x1) + (-5x1)

 

= 9 - (-3) + (-5)

 

= 7

 

Hence Log1,000,000,000 +  log 0.001 + log₃243 = 7

 

TRY THIS……………..

 

 

Evaluate Log1,000,000,000  -   log 0.0001 + log₃81

VARIATIONS F1

 

x is inversely proportional to y. x=22 while y=5. Find y when x is 10.

 

Solution

 

x ⍺ k

      y

 

x = k

      y

 

22 = k

        5

 

k = 22 x 5

 

k = 110

 

,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,

 

k = 110, y= ?, x = 10.

 

x = k

      y

 

10  = 110

          y

 

y x 10 = 110  x  y   (multiply by y on both sides)

               y

 

 

10y = 110

10      10

 

Hence y = 11.

 

 

TRY THIS…………….

 

 

x is inversely proportional to y. x=80 while y=4. Find y when x is 8. 

LOGARITHMS F8

 

Simplify Log₂256 - Log₃729

 

Solution

 

= Log₂256 - Log₃729

 

= Log₂2⁸ - Log₃3⁵    [Since 256=2⁸ and 729=3⁶].

 

= 8Log₂2 - 6Log₃3    [since Log_aa = 1]

 

= (8 x 1) - (6 x 1)

 

= 8 - 6

 

= 2

 

Hence Log₂256 -Log₃729 = 2

 

TRY THIS..................

 

Simplify Log₂2048 - Log₅625 

LENGTH OF AN ARC F1

 

Find the length of an arc if the radius of the circle is 70cm.

 

Solution

 

L = ∏r

      180⁰

 

L = ∏ x  70

             180⁰

 

L = 7∏ cm

       18

 

Hence length of an arc is ^7∏/18 cm

 

TRY THIS…………………………..

 

 

Find the length of an arc if the radius of the circle is 30cm.

COMPOUND INTEREST F1

Mwakajonga invested a certain amount of money in a bank which gives an interest rate of 20% compounded annually. How much did she invest at the start if she got 20,000 sh at the end of 3 years?

 

Solution

 

n=3, t=1, R=20%, A₃=8,500, P=?

A_n = P(1 + ^RT/100)ⁿ

A₃ = P(1 + ^(20x1)/100)³

A₃= P(1 + ²⁰/100)³

A₃ = P(¹⁰⁰/100 + ²⁰/100)³

A₃ = P(¹²⁰/100)³  But A₃=20,000.

20,000 = P(1.2)³  = P(1.2x1.2x1.2)  

 

20,000 = 1.728P

 

20000  =  1.728P

1.728       1.728

 

20000  =  P

1.728

 

P ≈ 11574/=

 

Hence at the start she invested Tsh 11574/=

 

TRY THIS………………..

 

 

Tunsubilege invested a certain amount of money in a bank which gives an interest rate of 20% compounded annually. How much did she invest at the start if she got 16,000 sh at the end of 5 years?

EXPAND F1

 

Expand 11w(5w + 3 - 11w)

 

Solution

 

= 11w(5w + 3 - 11w)

 

= (11w x 5w) + (11w x 3) - (11w x 11w)

 

= 55w² + 33w - 121w²

 

= [55w² - 121w²] + 33w collecting like terms

 

= - 66w² + 33w

 

= 33w - 66w² answer

 

 

TRY THIS………..

  

Expand 6a(5a+ 12 - 9a)

LOGARITHMS F7

 If log_x 2401 – log₃729 = -2; find x

 

solution

 

log_x 2401 – log₃729 = -2

 

log_x 2401 – log₃3⁶ = -2

 

log_x 2401 – 6log₃3 = -2

 

log_x 2401 – 6 x 1 = -2

 

log_x 2401 – 6 = -2

 

log_x 2401 = -2 + 6

 

log_x 2401 = 4 

 

2401 = x⁴        2401=7x7x7x7=7⁴ by prime factors

 

7⁴ = x⁴      Powers cancel out

 

x = 7

 

Hence x = 7.