Question 1112870
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For 1/3 of the lemons he paid 4p each, for the other 2/3 he paid 3p each.  That means he bought twice as many at 3p each as he bought at 4p each.<br>
So consider "packages" of 1 lemon at 4p and 2 lemons at 3p each.  Each of those packages costs 10p, so for £5 he can buy 50 of those packages.<br>
Since there are 3 lemons in each package, the number of lemons he bought was 50*3 = 150.<br>
Algebraically....<br>
Let x be the total number of lemons.
Then he bought (1/3)x lemons at 4p each and (2/3)x lemons at 3p each; and the total cost was £5 = 500p.  So<br>
{{{(1/3)x*4 + (2/3)x*3 = 500}}}
{{{(4/3)x+2x = 500}}}
{{{(10/3)x = 500}}}
{{{x = 500*(3/10) = 150}}}