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If a−6b+6c=4a - 6b + 6c = 4 and 6a+3b−3c=506a + 3b - 3c = 50, where aa, bb and cc are real numbers, the value of 2a+3b−3c2a + 3b - 3c is

Solution

✅ Correct Option: 2

Look at what we're asked to find: 2a+3b−3c2a + 3b - 3c.

Notice that 3b−3c=3(b−c)3b - 3c = 3(b - c). Now glance at the given equations:

a−6b+6c=4  ⟹  a−6(b−c)=4⋯(1)a - 6b + 6c = 4 \implies a - 6(b - c) = 4 \quad \cdots (1)

6a+3b−3c=50  ⟹  6a+3(b−c)=50⋯(2)6a + 3b - 3c = 50 \implies 6a + 3(b - c) = 50 \quad \cdots (2)

See how bb and cc always appear together as (b−c)(b - c)? That means we don't need to find bb and cc individually — we only need (b−c)(b - c) and aa.


From Equation (1)(1):

a=4+6(b−c)⋯(3)a = 4 + 6(b - c) \quad \cdots (3)

Substitute into Equation (2)(2):

6[4+6(b−c)]+3(b−c)=506[4 + 6(b - c)] + 3(b - c) = 50

24+36(b−c)+3(b−c)=5024 + 36(b - c) + 3(b - c) = 50

39(b−c)=2639(b - c) = 26

b−c=2639=23b - c = \dfrac{26}{39} = \dfrac{2}{3}


Plug b−c=23b - c = \dfrac{2}{3} back into Equation (3)(3):

a=4+6×23=4+4=8a = 4 + 6 \times \dfrac{2}{3} = 4 + 4 = 8


2a+3b−3c=2a+3(b−c)2a + 3b - 3c = 2a + 3(b - c)

=2(8)+3 ⁣(23)= 2(8) + 3\!\left(\dfrac{2}{3}\right)

=16+2= 16 + 2

=18= \boxed{18}

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