Q.If \( (7a - 5b) : (3a + 4b) = 7 : 11 \), then what is the value of \( (5a - 3b) : (6a + 5b) \)? (a) 777:244 (b) 777:247 (c) 247:778 (d) 247:787
Answer: C
Given: \[ (7a - 5b) : (3a + 4b) = 7 : 11 \] Or, \[ \frac{7a - 5b}{3a + 4b} = \frac{7}{11} \] Cross-multiplying: \[ 77a - 55b = 21a + 28b \] Rearranging: \[ 77a - 21a = 28b + 55b \] \[ 56a = 83b \] So, \[ a = \frac{83b}{56} \] Now, \[ (5a - 3b) : (6a + 5b) \] Substitute \( a = \frac{83b}{56} \): \[ = 5 \times \frac{83b}{56} - 3b : 6 \times \frac{83b}{56} + 5b \] \[ = \frac{415b - 168b}{56} : \frac{498b + 280b}{56} \] \[ = \frac{247b}{56} : \frac{778b}{56} \] \[ = 247b : 778b \] \[ = 247 : 778 \]
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