Justin had some cranberry biscuits and strawberry biscuits. ⁵₇ of the number of cranberry biscuits was equal to ¹₅ of the number of strawberry biscuits. After Justin made 21 more cranberry biscuits, the number of cranberry biscuits was ²₅ of the number of strawberry biscuits. How many biscuits did he have altogether in the end?
Make the numerators the same. LCM of 5 and 1 is 5.

57 of cranberry biscuits = 1x55x5 of strawberry biscuits

⁵₇ of cranberry biscuits = ⁵₂₅ of strawberry biscuits

	Cranberry biscuits	Strawberry biscuits	Total
Before	7 u	25 u
Change	+ 21
After	2x5 = 10 u	5x5 = 25 u	35 u

The number of strawberry biscuits remains unchanged.  Make the number of strawberry biscuits the same.  LCM of 5 and 25 is 25.

Number of more cranberry biscuits made
= 10 u - 7 u
= 3 u

3 u = 21

1 u = 21 ÷ 3 = 7

Number of biscuits that Justin had in the end
= 10 u + 25 u
= 35 u
= 35 x 7
= 245

Answer(s): 245