Question

Sister can bake 50 cakes in 25 hours, Sister and Mummy together can bake 75 cakes in 15 hours. How many cakes Mummy can bake in 15 hours?

A) 25 B) 45 C) 20 D) 10

Answer 1

Answer:

B) is the correct answer

Step-by-step explanation:

sister can bake cakes in one hour =50÷25

=2

sister can bake cakes in 15 hours =2×15

=30

Mummy can bake cakes in 15 hour=75-30

=45

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Answer 2

In 15 hours mummy can bake 45 cakes.

Option B is correct.

Given:

• Sister can bake 50 cakes in 25 hours.
• Sister and Mummy together can bake 75 cakes in 15 hours.

To find:

• How many cakes Mummy can bake in 15 hours?

• A) 25
• B) 45
• C) 20
• D) 10

Solution:

Concept to be used:

• Apply unitary method.

Step 1:

Find the time taken to bake one cake by sister.

ATQ,

Sister can bake 50 cakes in 25 hours.

1 cake was baked in $\frac{25}{50} \: hours$

$= \frac{1}{2} \: hour$

Or,

We can say, sister can bake one cake in 30 minutes.

Step 2:

Find the time taken by both mummy and sister to bake one cake.

ATQ,

Sister and Mummy together can bake 75 cakes in 15 hours.

Mummy and sister can bake one cake in $\frac{15}{75} \: hours$

$= \frac{1}{5} \: hours$

Therefore,

Both can bake one cake in 12 minutes.

Step 3:

Find the time taken by mummy alone to bake one cake.

Let mummy can alone bake one cake in 'x' minutes.

$\frac{1}{30} + \frac{1}{x} = \frac{1}{12}$

$\frac{1}{x} = \frac{1}{12} - \frac{1}{30}$

$\frac{1}{x} = \frac{3}{60}$

or

$\bf x = 20 \: min$

So,

Mummy can bake one cake in 20 minutes.

Step 4:

Find the number of cake baked by mummy.

One cake is baked in 20 minutes.

So,

In one hour mummy can bake 3 cakes.

In 15 hours mummy can bake $=3 \times 15$

=45 cakes

Thus,

In 15 hours mummy can bake 45 cakes.

Option B is correct.

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