If a = 2 and b = 5, the value of the expression 2a-[3a+{4b-(2a-b)+5a}-7b] is :

Answer

To solve the expression \( 2a - [3a + \{ 4b - (2a - b) + 5a \} - 7b] \) given \( a = 2 \) and \( b = 5 \), we will follow these steps:

### Step 1: Substitute the values of \( a \) and \( b \)

Substituting \( a = 2 \) and \( b = 5 \) into the expression:

\[ 2(2) - [3(2) + \{ 4(5) - (2(2) - 5) + 5(2) \} - 7(5)] \]

### Step 2: Calculate the values inside the brackets

Calculating the values step by step:

1. Calculate \( 2(2) \):
\[ 2(2) = 4 \]

2. Calculate \( 3(2) \):
\[ 3(2) = 6 \]

3. Calculate \( 4(5) \):
\[ 4(5) = 20 \]

4. Calculate \( 7(5) \):
\[ 7(5) = 35 \]

Now, substitute these values back into the expression:

\[ 4 - [6 + \{ 20 - (4 - 5) + 10 \} - 35] \]

### Step 3: Solve the innermost bracket

Now, solve the innermost bracket \( (4 - 5) \):
\[ 4 - 5 = -1 \]

So, we have:

\[ 4 - [6 + \{ 20 - (-1) + 10 \} - 35] \]

### Step 4: Simplify the curly bracket

Now, simplify the curly bracket:

\[ 20 - (-1) = 20 + 1 = 21 \]

So, we have:

\[ 4 - [6 + \{ 21 + 10 \} - 35] \]

Now, simplify \( 21 + 10 \):
\[ 21 + 10 = 31 \]

Now substitute back:

\[ 4 - [6 + 31 - 35] \]

### Step 5: Simplify the square bracket

Now, simplify the square bracket:

\[ 6 + 31 = 37 \]
\[ 37 - 35 = 2 \]

So, we have:

\[ 4 - [2] \]

### Step 6: Final calculation

Now, perform the final calculation:

\[ 4 - 2 = 2 \]

Thus, the value of the expression is:

\[ \boxed{2} \]